TY - JOUR. T1 - Ab initio quantum mechanical/molecular mechanical molecular dynamics simulation of enzyme catalysis. T2 - The case of histone lysine methyltransferase SET7/9. AU - Wang, Shenglong. AU - Hu, Po. AU - Zhang, Yingkai. PY - 2007/4/12. Y1 - 2007/4/12. N2 - To elucidate enzyme catalysis through computer simulation, a prerequisite is to reliably compute free energy barriers for both enzyme and solution reactions. By employing on-the-fly Born-Oppenheimer molecular dynamics simulations with the ab initio quantum mechanical/molecular mechanical approach and the umbrella sampling method, we have determined free energy profiles for the methyl-transfer reaction catalyzed by the histone lysine methyltransferase SET7/9 and its corresponding uncatalyzed reaction in aqueous solution, respectively. Our calculated activation free energy barrier for the enzyme catalyzed reaction is 22.5 kcal/mol, which agrees very well with the experimental value of 20.9 kcal/mol. The difference in potential of mean ...
TY - JOUR. T1 - Serine protease acylation proceeds with a subtle re-orientation of the histidine ring at the tetrahedral intermediate. AU - Zhou, Yanzi. AU - Zhang, Yingkai. PY - 2011/2/7. Y1 - 2011/2/7. N2 - The acylation mechanism of a prototypical serine protease trypsin and its complete free energy reaction profile have been determined by Born-Oppenheimer ab initio QM/MM molecular dynamics simulations with umbrella sampling.. AB - The acylation mechanism of a prototypical serine protease trypsin and its complete free energy reaction profile have been determined by Born-Oppenheimer ab initio QM/MM molecular dynamics simulations with umbrella sampling.. UR - http://www.scopus.com/inward/record.url?scp=78751489563&partnerID=8YFLogxK. UR - http://www.scopus.com/inward/citedby.url?scp=78751489563&partnerID=8YFLogxK. U2 - 10.1039/c0cc04112b. DO - 10.1039/c0cc04112b. M3 - Article. C2 - 21116528. AN - SCOPUS:78751489563. VL - 47. SP - 1577. EP - 1579. JO - Chemical Communications. JF - Chemical ...
Molecular dynamics studies have been performed on the zwitterionic form of the dipeptide glycine-alanine in water, with focus oil the solvation and electrostatic properties using a range of theoretical methods, from purely classical force fields, through mixed quantum mechanical/molecular mechanical simulations, to fully quantum mechanical Car-Parrinello calculations. The results of these studies show that the solvation pattern is similar for all methods used for most atoms in the dipeptide, but call differ substantially for some groups; namely the carboxy and aminoterminii, and the backbone amid NH group. This might have implications in other theoretical studies of peptides and proteins, with charged -NH3+ and -CO2- side chains solvated in water. Hybrid quantum mechanical/molecular mechanical simulations successfully reproduce the solvation patterns from the fully quantum mechanical simulations (PACS numbers: 87.14.Ee, 87.15.Aa, 87.15.He. 71.15.Pd). ...
Ornithine cyclodeaminase (OCD) is an NAD+-dependent deaminase that is found in bacterial species such as Pseudomonas putida. Importantly, it catalyzes the direct conversion of the amino acid L-ornithine to L-proline. Using molecular dynamics (MD) and a hybrid quantum mechanics/molecular mechanics (QM/MM) method in the ONIOM formalism, the catalytic mechanism of OCD has been examined. The rate limiting step is calculated to be the initial step in the overall mechanism: hydride transfer from the L-ornithines Cα-H group to the NAD+ cofactor with concomitant formation of a Cα=NH2+ Schiff base with a barrier of 90.6 kJ mol−1. Importantly, no water is observed within the active site during the MD simulations suitably positioned to hydrolyze the Cα=NH2+ intermediate to form the corresponding carbonyl. Instead, the reaction proceeds via a non-hydrolytic mechanism involving direct nucleophilic attack of the δ-amine at the Cα-position. This is then followed by cleavage and loss of the α-NH2 group to give
wp-content/uploads/2017/10/blank-box.png 0 0 admin /wp-content/uploads/2017/10/blank-box.png admin2015-01-16 20:47:322015-02-17 21:23:51Quantum mechanical/molecular mechanical study of the HDV ribozyme: Impact of the catalytic metal ion on the mechanism ...
Calculations have been performed on the entire Fe(Schiff base) · cdHO system using the QM/MM ONIOM (DFT : AMBER) method implemented in Gaussian 09 [29]. The charges and protonation states of all titrable amino acids were automatically assigned using the interface provided by the UCSF Chimera package [30] with the exception of the iron-chelating histidine His20, which was manually set to be consistent with the coordination rules of the metal. Visual inspection was subsequently performed. The total charge of the system is −8 or −7 depending on the oxidation state of the iron. It can be divided by −10 for the isolated protein and +2 or +3 for the inorganic complex. The QM part in the QM/MM partition has a charge +1 in the Fe(II) species and +2 for the Fe(III) ones.. One of the main objectives of this work is to determine whether the experimental structure corresponds to a plausible electronic structure of the metal centre in a resting state configuration or not. Thus, we are interested in ...
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Abstract: Well-developed conventional single-reference electron-correlation methods usually fail to describe the dissociation of covalent bonds, di(or poly)radical systems or electronic structures of the excited states. Based on a multi-determinantal wave function, recently emerged multireference perturbation theories and coupled cluster theories can give drastically improved results; however, there is still no satisfactory scheme so far. In this monograph, alternative multireference perturbation theories and coupled cluster theories based on the block-correlation framework has been introduced and illustrated in detail, together with proper comparisons with other common electron-correlation methods. Future perspectives upon multireference theories have also been briefly discussed.. Key words: Multireference, Block-correlated perturbation theory, Block-correlated coupled cluster theory, Multiple bond dissociation, Energy potential surface ...
TY - JOUR. T1 - Self-trapping properties and recurrence phenomena in a modified discrete non-linear Schrodinger equation. AU - Kalosakas, G.. AU - Tsironis, G. P.. AU - Economou, E. N.. PY - 1994/12/1. Y1 - 1994/12/1. N2 - We study the properties of a modified discrete non-linear Schrodinger equation (MDNLS) that arises from the coupling of an excitation to an acoustic chain. We find exact results for self-trapping in chains of two and three sites and approximate results for longer chains. We also study possible recurrence phenomena in the equation and compare our findings with those of the standard DNLS as well as the integrable DNLS. We find that dynamics in MDNLS becomes more rapidly irregular compared to the other two equations.. AB - We study the properties of a modified discrete non-linear Schrodinger equation (MDNLS) that arises from the coupling of an excitation to an acoustic chain. We find exact results for self-trapping in chains of two and three sites and approximate results for ...
You may have read that quantum computers one day could break most current cryptography systems. They will be able to do that because there are some very clever algorithms designed to run on quantum computers that can solve a hard math problem, which in turn can be used to factor very large numbers. One of the most famous is Shors Factoring Algorithm. The difficulty of factoring large numbers is essential to the security of all public-private key systems - which are the most commonly used today. Current quantum computers dont have nearly enough qubits to attempt the task, but various experts predict they will within the next 3-8 years. That leads to some potentially dangerous situations, such as if only governments and the super-rich had access to the ultra-secure encryption provided by quantum computers ...
Read Multiple network alignment on quantum computers, Quantum Information Processing on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips.
Electronic spectra of guanine in the gas phase and in water were studied by quantum mechanical/molecular mechanical (QM/MM) methods. Geometries for the excited-state calculations were extracted from ground-state molecular dynamics (MD) simulations using the self-consistent-charge density functional tight binding (SCC-DFTB) method for the QM region and the TIP3P force field for the water environment. Theoretical absorption spectra were generated from excitation energies and oscillator strengths calculated for 50 to 500 MD snapshots of guanine in the gas phase (QM) and in solution (QM/MM). The excited-state calculations used time-dependent density functional theory (TDDFT) and the DFT-based multireference configuration interaction (DFT/MRCI) method of Grimme and Waletzke, in combination with two basis sets. Our investigation covered keto-N7H and keto-N9H guanine, with particular focus on solvent effects in the low-energy spectrum of the keto-N9H tautomer. When compared with the vertical excitation ...
The mission of QICI is to promote the growth of the quantum information area in Hong Kong, and to develop Hong Kong as an international research hub for quantum information and computation. QICI has been established in November 2018 under the auspices of the HKU Department of Computer Science. Its research platform consists of 3 research teams working on quantum information theory, quantum cryptography, quantum gravity, and quantum foundations. ...
The research is oriented toward the Density Functional Theory (DFT) based dissection of catalytic mechanism (transition state and possible intermediate structures) of proteins containing metallic cofactors, as well as of their synthetic models. Particular interest is devoted to the mechanism of activation of small molecules such as hydrogen (H2) and hydrogen peroxide (H2O2). The former activity is performed by hydrogenases (Fe-Fe and Ni-Fe, according to the different ions being in the cofactor) whereas the latter is carried out by vanadium haloperoxidase (VHPO). Quantum Mechanics (QM) tools and hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) represent a valid resource to elucidate possible speciation forms in solution of synthetic models of enzymes, permit rationalization at molecular level of experimentally observed lower activity of synthetic models with respect to the natural bio-system. Furthermore they can help in showing alternative routes for catalytic productions and in elucidating ...
The research is oriented toward the Density Functional Theory (DFT) based dissection of catalytic mechanism (transition state and possible intermediate structures) of proteins containing metallic cofactors, as well as of their synthetic models. Particular interest is devoted to the mechanism of activation of small molecules such as hydrogen (H2) and hydrogen peroxide (H2O2). The former activity is performed by hydrogenases (Fe-Fe and Ni-Fe, according to the different ions being in the cofactor) whereas the latter is carried out by vanadium haloperoxidase (VHPO). Quantum Mechanics (QM) tools and hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) represent a valid resource to elucidate possible speciation forms in solution of synthetic models of enzymes, permit rationalization at molecular level of experimentally observed lower activity of synthetic models with respect to the natural bio-system. Furthermore they can help in showing alternative routes for catalytic productions and in elucidating ...
Polymer quantum systems are mechanical models quantized similarly as loop quantum gravity. It is actually in quantizing gravity that the polymer term holds proper as the quantum geometry excitations yield a reminiscent of a polymer material. In such an approach both non-singular cosmological models and a microscopic basis for the entropy of some black holes have arisen. Also important physical questions for these systems involve thermodynamics. With this motivation, in this work, we study the statistical thermodynamics of two one dimensional polymer quantum systems: an ensemble of oscillators that describe a solid and a bunch of non-interacting particles in a box, which thus form an ideal gas. We first study the spectra of these polymer systems. It turns out useful for the analysis to consider the length scale required by the quantization and which we shall refer to as polymer length. The dynamics of the polymer oscillator can be given the form of that for the standard quantum pendulum. ...
Recent devices, using hundreds of superconducting quantum bits, claim to perform quantum computing. However, it is not an easy task to determine and quantify the degree of quantum coherence and control used by these devices. Namely, it is a difficult task to know with certainty whether or not a given device (e.g., the D-Wave One or D-Wave Two) is a quantum computer. Such a verification of quantum computing would be more accessible if we already had some kind of working quantum computer, to be able to compare the outputs of these various computing devices. Moreover, the verification process itself could strongly depend on whether the tested device is a standard (gate-based) or, e.g., an adiabatic quantum computer. Here we do not propose a technical solution to this quantum-computing
Filling the lowest quantum state of the conduction band (CB) of colloidal nanocrystals with a single electron, which is analogous to the filling the lowest unoccupied molecular orbital (LUMO) in a molecule with a single electron, has attracted much attention due to the possibility of harnessing the electron spin for potential spin-based applications. The quantized energy levels of the artificial atom, in principle, make it possible for a nanocrystal to be filled with an electron if the Fermi-energy level is optimally tuned during the nanocrystal growth. Here, we report the singly occupied quantum state (SOQS) and doubly occupied quantum state (DOQS) of a colloidal nanocrystal in steady state under ambient conditions. The number of electrons occupying the lowest quantum state can be controlled to be zero, one (unpaired) and two (paired) depending on the nanocrystal growth time via changing the stoichiometry of the nanocrystal. Electron paramagnetic resonance spectroscopy (EPR) proved the ...
This is the draft version of a textbook, which aims to introduce the quantum information science viewpoints on condensed matter physics to graduate students in physics (or interested researchers). We keep the writing in a self-consistent way, requiring minimum background in quantum information science. Basic knowledge in undergraduate quantum physics and condensed matter physics is assumed. We start slowly from the basic ideas in quantum information theory, but wish to eventually bring the readers to the frontiers of research in condensed matter physics, including topological phases of matter, tensor networks, and symmetry-protected topological phases ...
The solutions quantum mechanics and path integrals solutions manual have been made possible by two major advances. In order to observe a specific path one needs to design an appropriate observable. Liboff Quantum Mechanics Solution Manual introductory quantum mechanics by liboff solution manual Problems in Quantum Mechanics: With SolutionsQuantum Mechanics: Concepts and Applications Nouredine Zettili on Amazon. We apply the method to the free particle and quantum harmonic oscillator, investigate the. Within either of these contexts, the text and derivations are crystal clear and highly pedagogic. Path Integrals in Quantum Mechanics Dennis V. Lecture Series on Quantum Mechanics from the University of Maryland. Path Integral 1 Feynmans Path Integral Formulation Feynmans formulation of quantum mechanics using the so-called path inte-gral is arguably the most elegant.. ) as well as specialized topics (scattering, dissipative systems, spin &92;& color in the path integral, lattice methods etc. We ...
The reaction of the potential anticancer drug kiteplatin, cis-[PtCl2(cis-1,4-DACH)], with oligomers of single- and double-stranded DNA ranging from 2 to 12 base pairs in length was performed as a model for DNA interaction. The potential for conformational flexibility of single-stranded adducts was examined with density functional theory (DFT) and compared with data from 1H-NMR 1D and 2D spectroscopy. This indicates the presence of multiple conformations of an adduct with d(GpG), but only one form of the adduct with d(TGGT). The importance of a suitable theoretical model, and in particular basis set, in reproducing experimental data is demonstrated. The DFT theoretical model was extended to platinated base pair step (GG/CC), allowing a comparison to the related compounds cisplatin and oxaliplatin. Adducts of kiteplatin with larger fragments of double-stranded DNA, including tetramer, octamer, and dodecamer, were studied theoretically using hybrid quantum mechanics/molecular mechanics methods. ...
TY - JOUR. T1 - Hydride transfer in liver alcohol dehydrogenase. T2 - Quantum dynamics, kinetic isotope effects, and role of enzyme motion. AU - Billeter, S. R.. AU - Webb, S. P.. AU - Agarwal, P. K.. AU - Iordanov, T.. AU - Hammes-Schiffer, S.. PY - 2001/11/14. Y1 - 2001/11/14. N2 - The quantum dynamics of the hydride transfer reaction catalyzed by liver alcohol dehydrogenase (LADH) are studied with real-time dynamical simulations including the motion of the entire solvated enzyme. The electronic quantum effects are incorporated with an empirical valence bond potential, and the nuclear quantum effects of the transferring hydrogen are incorporated with a mixed quantum/classical molecular dynamics method in which the transferring hydrogen nucleus is represented by a three-dimensional vibrational wave function. The equilibrium transition state theory rate constants are determined from the adiabatic quantum free energy profiles, which include the free energy of the zero point motion for the ...
The hemoprotein myoglobin is a model system for the study of protein dynamics. We used time-resolved serial femtosecond crystallography at an x-ray free-electron laser to resolve the ultrafast structural changes in the carbonmonoxy myoglobin complex upon photolysis of the Fe-CO bond. Structural changes appear throughout the protein within 500 femtoseconds, with the C, F, and H helices moving away from the heme cofactor and the E and A helices moving toward it. These collective movements are predicted by hybrid quantum mechanics/molecular mechanics simulations. Together with the observed oscillations of residues contacting the heme, our calculations support the prediction that an immediate collective response of the protein occurs upon ligand dissociation, as a result of heme vibrational modes coupling to global modes of the protein ...
Feb 4, 2020: In a measurement process, a quantum system is subject to an unavoidable back-action due to the quantum fluctuations of the detector. As a consequence, the system evolves along stochastic quantum trajectories. This features can be used as a tool to engineer and control quantum states, e.g. via feedback mechanisms, as well as to access new properties of open quantum systems. This is possible in actual experiments thanks to the degree of control of some quantum systems. In this talk, I present two application of quantum measurement. First, I will discuss the thermodynamics, i.e. the energy and information exchange, of a qubit coupled to a quantum detector [1]. In particular, I will show how information gained by tracking single quantum trajectories of the qubit can be converted into work using quantum coherent feedback. I show that quantum backaction can lead to a loss of information in imperfect measurements in a superconducting circuit. As a second example, I will show that a time-dependent
An implementation of Ewald summation for use in mixed quantum mechanics/molecular mechanics (QM/MM) calculations is presented, which builds upon previous work by others that was limited to semi-empirical electronic structure for the QM region. Unlike previous work, our implementation describes the wave functions periodic images using ChElPG atomic charges, which are determined by fitting to the QM electrostatic potential evaluated on a real-space grid. This implementation is stable even for large Gaussian basis sets with diffuse exponents, and is thus appropriate when the QM region is described by a correlated wave function. Derivatives of the ChElPG charges with respect to the QM density matrix are a potentially serious bottleneck in this approach, so we introduce a ChElPG algorithm based on atom-centered Lebedev grids. The ChElPG charges thus obtained exhibit good rotational invariance even for sparse grids, enabling significant cost savings. Detailed analysis of the optimal choice of ...
TY - JOUR. T1 - Density functional theory studies of chloroethene adsorption on zerovalent lron. AU - Lim, Dong Hee. AU - Lastoskie, Christian M.. AU - Soon, Aloysius. AU - Becker, Udo. PY - 2009/2/15. Y1 - 2009/2/15. N2 - Adsorption of perchloroethene (PCE), trichloroethene (TCE), and cis-dichloroethene (cis-DCE) on zerovalentiron is investigated using density functional theory (DFT) to evaluate hypotheses concerning the relative reactivity of these compounds on zerovalent iron. Four different chloroethene adsorption modes on the Fe(110) surface were studied using periodic DFT and the generalized gradient approximation (GGA). Of the adsorption sites examined, the atop site, where the chloroethene C=C bond straddles a surface iron atom, was the most energetically favorable site for the adsorption of all three chloroethenes. Electronic structure and property analyses provide an indication of the extent of sp 2-sp 3 hybridization. The strong hybridization of the π-bonding orbital between the ...
Abstract: Over the last century, a large number of physical and mathematical developments paired with rapidly advancing technology have allowed the field of quantum chemistry to advance dramatically. However, the lack of computationally efficient methods for the exact simulation of quantum systems on classical computers presents a limitation of current computational approaches. We report, in detail, how a set of pre-computed molecular integrals can be used to explicitly create a quantum circuit, i.e. a sequence of elementary quantum operations, that, when run on a quantum computer, to obtain the energy of a molecular system with fixed nuclear geometry using the quantum phase estimation algorithm. We extend several known results related to this idea and discuss the adiabatic state preparation procedure for preparing the input states used in the algorithm. With current and near future quantum devices in mind, we provide a complete example using the hydrogen molecule, of how a chemical Hamiltonian ...
Clients will have online access to the computing power of the first IBM Q systems by the end of 2017, with a series of planned upgrades during 2018. IBM is focused on making available advanced, scalable universal quantum computing systems to clients to explore practical applications. The latest hardware advances are a result of three generations of development since IBM first launched a working quantum computer online for anyone to freely access in May 2016. Within 18 months, IBM has brought online a 5 and 16 qubit system for public access through the IBM Q experience and developed the worlds most advanced public quantum computing ecosystem.. We are, and always have been, focused on building technology with the potential to create value for our clients and the world, said Dario Gil, vice president of AI and IBM Q, IBM Research. The ability to reliably operate several working quantum systems and putting them online was not possible just a few years ago. Now, we can scale IBM processors up to ...
Pour Elise Dumont, une chimiste française, elegante comme tous les françaises. The arrogant but brilliant physicist Paul Dirac, after solving one of the foundational problems of quantum mechanics, was alleged to have said ...the rest, is chemistry. Oh what weasely words they were. True, quantum chemistry can be seen as merely the solution of the Schrodinger equation, but what rich solutions! Dirac would not have known the dazzling complexity that was to take place in the field that would come to be known as quantum chemistry.. There have been, at times, heroic attempts to find tractable approximations to solve the Schrodinger equation for larger and larger molecules. Weve also realized that the Schrodinger equation is actually an insufficient principle to do chemistry because in the end, the Schrodinger equation is a single electron equation. Reality is made up of more than 1 electron. However, there does not exist an authoritative multi-electron theory, there are several competing ...
A randomized controlled trial was set up to test the hypothesis that the fertilization rate of oocytes after intracytoplasmic sperm injection (ICSI) is higher after immobilization of the spermatozoa with the Fertilase-laser system technology than after immobilization of the spermatozoa with the conventional mechanical method. Metaphase II oocytes were injected with spermatozoa that were immobilized with the conventional mechanical method (group A, n=177) or with spermatozoa that were immobilized with the Fertilase-laser system technology (group B, n=179). The fertilization rate per successfully injected oocyte was comparable in group A (62.6%; 92/147) and in group B (56.3%; 89/158)(p=0.3). No difference could be observed in fertilization rates of oocytes injected with spermatozoa that were immobilized with the Fertilase-laser system technology compared to spermatozoa immobilized with the conventional mechanical method ...
In the present study, the binding free energy of some classical inhibitors (DMT, DNP, GNT, HUP, THA) with acetylcholinesterase (AChE) is calculated by means of the free energy perturbation (FEP) method based on hybrid quantum mechanics and molecular mechanics (QM/MM) potentials. The results highlight the key role of the van der Waals interaction for the inhibition process, since the contribution of this term to the binding free energy is almost as decisive as the electrostatic one. The analysis of the geometrical parameters and the interaction energy per residue along the QM/MM molecular dynamics (MD) simulations highlights the most relevant interactions in the different AChE-ligand systems, showing that the charged residues with a more prominent contribution to the interaction energy are Asp72 and Glu199, although the relative importance depends on the molecular size of the ligand ...
Groundbreaking approach could impact fields from cryptography to materials science. In an important first for a promising new technology, scientists have used a quantum computer to calculate the precise energy of molecular hydrogen. This groundbreaking approach to molecular simulations could have profound implications not just for quantum chemistry, but also for a range of fields from cryptography to materials science.. One of the most important problems for many theoretical chemists is how to execute exact simulations of chemical systems, says author Alán Aspuru-Guzik, assistant professor of chemistry and chemical biology at Harvard University. This is the first time that a quantum computer has been built to provide these precise calculations.. The work, described this week in Nature Chemistry, comes from a partnership between Aspuru-Guziks team of theoretical chemists at Harvard and a group of experimental physicists led by Andrew White at the University of Queensland in Brisbane, ...
Quantum chemical calculations on the geometrical, conformational, spectroscopic (FTIR, FT-Raman) analysis and NLO activity of milrinone [5-cyano-2-methyl-(3,4-bipyridin)-6(1h)-one] by using hartree-fock and density functional methods
Accurate and efficient control of quantum systems is one of the central challenges for quantum information processing. Current state-of-the-art experiments rarely go beyond 10 qubits and in most cases demonstrate only limited control. Here we demonstrate control of a 12-qubit system, and show that the system can be employed as a quantum processor to optimize its own control sequence by using measurement-based feedback control (MQFC). The final product is a control sequence for a complex 12-qubit task: preparation of a 12-coherent state. The control sequence is about 10% more accurate than the one generated by the standard (classical) technique, showing that MQFC can correct for unknown imperfections. Apart from demonstrating a high level of control over a relatively large system, our results show that even at the 12-qubit level, a quantum processor can be a useful lab instrument. As an extension of our work, we propose a method for combining the MQFC technique with a twirling protocol, to optimize the
Use of Genetic Algorithm for Quantum Information Processing by NMR V.S. Manu and Anil Kumar Centre for quantum Information and Quantum Computing Department of Physics and NMR Research Centre Indian Institute of Science, Bangalore-560012. The Genetic Algorithm. John Holland. Slideshow 6634576 by kalia-delacruz
TY - JOUR. T1 - Density Functional Theory study of alloy interstitials in Al. AU - Klaver, Peter. AU - Chen, J.H.. PY - 2003. Y1 - 2003. M3 - Article. VL - 10. SP - 155. EP - 162. JO - Journal of Computer-Aided Materials Design. JF - Journal of Computer-Aided Materials Design. SN - 0928-1045. ER - ...
DFT and Quantum Chemical Studies for Heterocyclic Compounds, 978-3-659-21601-5, 9783659216015, 3659216011, Inorganic chemistry , The study of corrosion processes and their inhibition by organic inhibitors is a very active field of research. The presence of nitrogen, oxygen, phosphorous and sulphur in the organic molecules has a major effect on the inhibition efficiency and consequently on the phenomenon of adsorption on some metals surface. A great number of heterocyclic compounds were found to be excellent inhibitors of copper and steel corrosion. The inhibition effect mainly depends on some physicochemical and electronic properties of the organic inhibitor which relate to its functional groups, steric effects, electronic density of donor atoms, and orbital character of donating electrons. DFT Quantum chemical methods have already proven to be very useful in determining the molecular structure as well as elucidating the electronic structure and reactivity. Thus, it has become a common practice to
A series of density functional theory (DFT) and quantum mechanics/molecular mechanics (QM/MM) calculations are used to investigate the binding of platinum and ruthenium anticancer drugs to DNA. The qualitative and quantitative features of Beckes half-and-half (BHandH) functional for calculating geometries, binding energies and harmonic frequencies of non- covalently bound systems are tested and the intermolecular interactions are characterised and quantified using the QTAIM electron densities. Application of this DFT-QTAIM approach to complexes of the type (n6-arene)Ru(en)(nucleobase) 2+ shows a clear preference for binding at guanine over any other base both in gas phase and in aqueous solution, a trend explained on the basis of QTAIM and molecular orbital data. Key parameters of the QM/MM methodology within the ONIOM scheme and efficient geometry optimisation strategies are examined for applications involving DNA oligonucleotides. Calculations on cis- Pt(NH3)2 2+ (cisplatin) bound to ...
We present an investigation of optimal control techniques applied to computational and transport processes in the field of quantum information. We implement these processes using a range of different quantum systems: a harmonic oscillator, a pair of trapped Rydberg atoms, and a spin chain. In each case, we explore how application of analytic and numerical optimal control techniques (such as the Krotov method) can effect fast, efficient, and error-free unitary operations and information transfer processes, with particular attention to experimental uncertainties present in such systems and their implementations. In the pursuit of fast quantum operations, we discover that in our spin chain system our optimal control algorithm will fail to find solutions as the total operation time falls below a critical value. We postulate a correspondence between this value and that of the quantum speed limit, which defines a physical bound on the allowed rate of information transfer in quantum sytems when given a ...
Within the Born-Oppenheimer picture of the electronic Schrödinger equation the external potential due to the nuclei influences the resulting expectation values during the self consistent field procedure. In this thesis, the optimization and the benefit of atom centered potentials for an improved description and design of molecules is studied using density functional theory (DFT). It is shown that atom centered potentials can be used to increase the accuracy of the description of molecular properties as well as to generally explore chemical space rationally for structures which exhibit desired properties. The wide range of possible applications is illustrated by addressing several issues. First, an automated procedure is proposed for the design of optimal link pseudopotentials for quantum mechanics/molecular mechanics calculations. Secondly, it is shown how to tune variationally atom centered potentials within density functional perturbation theory in order to minimize the deviation in electron density
In this talk, we present our recent development of a rigorous framework which is based on the Feynman-Venron path integral formalism for open quantum systems. By resorting on quantum fields to describe the quantum excitation dynamics and taking the classical limit for the molecular degrees of freedom, we are able to analytically perform the path integral over the heat-bath and olecular vibrations. As a result, the matrix elements of the density matrix are described by an effective field theory for the quantum degrees of freedom only, and can be computed in perturbation theory, using appropriate Feynman rules. Extension to non-perturbative approximative approaches is alsodiscussed. As an illustrative example, we will apply this approach to study quantum transport and de-coherence in a simple model for an organic conjugate polymer.. ...
Löwdin appeared on the scene when quantum chemistry had already a very rich history and with his work as well as his initiatives gave it a further dynamism. Rather than reiterate some of the landmarks of the history of quantum chemistry prior to Löwdin, which are more or less well known to the readers of this journal, we would like to present these developments in a different manner. The following reflects ways historians approach their subject matter and, more specifically, our own approach, which attempts to articulate a framework where the history of quantum chemistry can be narrated not in a strict chronological order.[5] It appears that a host of interesting developments concerning the development of quantum chemistry-a classic case of an in-between discipline-can be narrated through six interrelated clusters of issues that manifest the particularities of its evolving (re)articulations with chemistry, physics, mathematics, and biology, as well as its institutional positioning. We, ...
The path integral formulation of time-dependent quantum mechanics provides the ideal framework for rigorous quantum-classical or quantum-semiclassical treatments, as the spatially localized, trajectory-like nature of the quantum paths circumvents the need for mean-field-type assumptions. However, the number of system paths grows exponentially with the number of propagation steps. In addition, each path of the quantum system generally gives rise to a distinct classical solvent trajectory. This exponential proliferation of trajectories with propagation time is the quantum-classical manifestation of time nonlocality, familiar from influence functional approaches. A quantum-classical path integral (QCPI) methodology has been developed. The starting point is the identification of two components in the effects induced on a quantum system by a polyatomic environment. The first, classical decoherence mechanism dominates completely at high temperature/low-frequency solvents and/or when the ...
The emergence of quantum computers has brought an unprecedented opportunity for quantum algorithm development and applications in quantum chemistry, quantum simulation, machine learning, cryptography, etc. On universal quantum computers, quantum algorithms can offer exponential speed-ups compared with conventional approaches, yet with significant hardware and algorithmic challenges remaining. Since noisy, small-to-intermediate scale quantum computers (NISQ) are around the corner, it is now critical to innovate quantum algorithms for such devices. One example, compiler development, will require innovation that bridges quantum physics, statistics, applied mathematics, and hardware and software design. The compiler is comprised of algorithms that assemble possible physical realizations of a logical operator acting on physical qubits, and then use the error characteristics of qubits (ion or superconducting circuits) to optimize the choice of realization for this architecture. Quantum computing is ...
Performing quantum chemistry investigations for groups of experimentalists, I have found that quite often the theoretical and experimental methods give different realities, not intersecting each other. This means that if experimental methods are used, for example, to investigate a mechanism of a chemical reaction, or the dependence of experimentally obtained data on some structural properties of the molecules, these methods often lead to wrong conclusions. The quantum chemistry methods disprove these conclusions, but often do not give an alternative, because, as mentioned above, the quantum chemistry is of quite limited applied use. Maybe in the future these realities will intersect, and then the main method of investigations will be the combination of quantum chemistry with the experimental methods ...
A new study from Yale University shows that scientists can create and control a large quantum mechanical system built on photons, suggesting that they might be able to expand the role of photons in quantum information systems.. Light might be able to play a bigger, more versatile role in the future of quantum computing, according to new research by Yale University scientists.. A team of Yale physicists has coaxed an unprecedented number of light particles, or photons, to behave quantum mechanically, or to assume more than one state simultaneously, such as alive and dead. In this case, the light is in the form of trapped microwave photons. Control over a greater number of photons - more than 100 in this case - raises the possibility that such states of light could play the part of several quantum bits (qubits), the building blocks typically found in a quantum computer. This could potentially minimize the physical scale and cost of building one.. The quantum computer, a still embryonic ...
In this paper we review a number of recent developments in the study of quantum tomography which is one of the useful methods for quantum state estimation and quantum information acquisition, having sparked explosion of interest in recent years. The quantum process tomography is also analyzed. At the same time, some success experiments and applications of quantum tomography are introduced. Finally, a number of open problems and future directions in this field are proposed.
Quantum computers, although not yet available on the market, will revolutionise the future of information processing. Already now, quantum computers of special purpose, i.e., quantum simulators, are within reach. The physics of ultracold atoms, ions, and molecules offers unprecedented possibilities of control of quantum many systems, and novel possibilities of applications for quantum information and quantum metrology. Particularly fascinating is the possibility of using ultracold atoms in lattices to simulate condensed matter or even high energy physics. This book provides a comprehensive overview of ultracold lattice gases as quantum simulators, an interdisciplinary field involving atomic, molecular, and optical physics; quantum optics; quantum information; and condensed matter and high energy physics. It includes some introductory chapters on basic concepts and methods, and focuses on the physics of spinor, dipolar, disordered, and frustrated lattice gases, before reviewing in detail artificial
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Quantum computers and Bitcoin. Quantum computers primarily perform calculations based on the probability of an objects state, even before it is measured.