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Ab initio simulation of the sum-frequency generation response of optically active liquids in the presence of a dc electric field —determination of the absolute molecular configuration

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Science China Chemistry 2014年第10期57卷 1405-1408页

作者： CHAMPAGNE Benot QUINET Olivier Laboratoire de Chimie Théorique Unité de Chimie Physique Théorique et Structurale Université de Namur

Quantum chemical computations have been performed to evaluate the first and second hyperpolarizability quantities of the interference term, linear in the external static electric field, that appear in the electric field-induced sum-frequency generation signal of chiral liquids. These are performed at the time-dependent Hartree-Fock level on the prototypical 1,1′-bi-2-naphtol chiral species.

关键词： second and third hyperpolarizabilities chirality nonlinear optics time-dependent Hartree-Fock

The Fourier space restricted Hartree-Fock method for the electronic structure calculation of linear poly(tetrafluoroethylene)

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Science China Chemistry 2014年第10期57卷 1355-1362页

作者： FRIPIAT Joseph G. HARRIS Frank E. Laboratoire de Chimie Théorique Unité de chimie physique théorique et structurale University of NamurRue de Bruxelles department of Physics University of Utah Quantum Theory Project University of Florida

Building on the pioneering work of Jean-Marie Andre and working in the laboratory he founded, the authors have developed a code called FT-1D to make Hartree-Fock electronic structure computations for stereoregular polymers using Ewald-type con- vergence acceleration methods. That code also takes full advantage of all line-group symmetries to calculate only the minimal set of two-electron integrals and to optimize the computation of the Fock matrix. The present communication reports a bench- mark study of the FT-1D code using polytetrafluoroethylene （PTFE） as a test case. Our results not only confirm the algorith- mic correctness of the code through agreement with other studies where they are applicable, but also show that the use of con- vergence acceleration enables accurate results to be obtained in situations where other widely-used codes （e.g., PLH and Crys- tal） fail. It is also found that full attention to the line-group symmetry of the PTFE polymer leads to an increase of between one and two orders of magnitude in the speed of computation. The new code can therefore be viewed as extending the range of electronic-structure computations for stereoregular polymers beyond the present scope of the successful and valuable code Crystal.

关键词： poly(tetrafluoroethylene) band structure Fourier-space Hartree-Fock lattice sum Ewaid

Comparison of reduced point charge models of proteins: Molecular Dynamics simulations of Ubiquitin

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Science China Chemistry 2014年第10期57卷 1340-1354页

作者： LEHERTE Laurence VERCAUTEREN Daniel P. Unité de Chimie Physique Théorique et Structurale Laboratoire de Physico-Chimie Informatique Namur MEdicine & Drug Innovation Center (NAMEDIC) Department of Chemistry University of Namur Rue de Bruxelles 61 B-5000 Namur Belgium

Reduced point charge models of amino acids are used to model Ubiquitin （PDB： 1UBQ）. They are designed （i） from local ex- tremum positions in charge density （CD） distribution functions built from the Poisson equation applied to smoothed molecular electrostatic potential functions, or （ii） from local maximum positions in promolecular electron density distribution （ED） func- tions. Charge values are fitted versus all-atom Amber99 molecular electrostatic potentials. The program GROMACS is used to generate molecular dynamics trajectories of the protein, under various implementation schemes, solvation, and temperature conditions. Point charges that are not located on atoms are considered as virtual sites with a null mass and radius. The results illustrate that secondary structure is best preserved with the CD-based model at low temperatures and in vacuum. This indi- cates that local potential energy wells are consistent with the all-atom model. However, at room temperature, the structure is best conserved when point charges are forced to be located on atoms, due to a better description of the Coulomb l-4 energy terms. The ED-based model, generated at a lower resolution, led to the largest discrepancies versus the all-atom case. The CD-based model allows the formation of protein-water H-bonds with geometrical properties similar to the all-atom ones. Con- trarily, intra-molecular H-bonds are not well described. Structural, thermodynamical, and dynamical properties of proteins modelled with reduced point charge models are also significantly affected by the choice of the solvent force field.

关键词： molecular electrostatic potential electron density smoothing of molecular fields critical points point charge model protein Ubiquitin