Search results for "quantum mechanics"
showing 10 items of 2468 documents
A quantum mechanics/molecular mechanics study of the protein-ligand interaction for inhibitors of HIV-1 integrase.
2007
Human immunodeficiency virus type-1 integrase (HIV-1 IN) is an essential enzyme for effective viral replication. Diketo acids such as L-731,988 and S-1360 are potent and selective inhibitors of HIV-1 IN. In this study, we used molecular dynamics simulations, within the hybrid quantum mechanics/molecular mechanics (QM/MM) approach, to determine the protein-ligand interaction energy between HIV-1 IN and L-731,988 and 10 of its derivatives and analogues. This hybrid methodology has the advantage that it includes quantum effects such as ligand polarisation upon binding, which can be very important when highly polarisable groups are embedded in anisotropic environments, as for example in metal-c…
Stimuli-responsive brushes with active minority components: Monte Carlo study and analytical theory
2015
Using a combination of analytical theory, Monte Carlo simulations, and three dimensional self-consistent field calculations, we study the equilibrium properties and the switching behavior of adsorption-active polymer chains included in a homopolymer brush. The switching transition is driven by a conformational change of a small fraction of minority chains, which are attracted by the substrate. Depending on the strength of the attractive interaction, the minority chains assume one of two states: An exposed state characterized by a stem-crown-like conformation, and an adsorbed state characterized by a flat two-dimensional structure. Comparing the Monte Carlo simulations, which use an Edwards-…
Competition between liquid-crystalline ordering and glassy freezing in melts of semiflexible polymers: A monte carlo simulation
1999
We present results of a Monte Carlo simulation of dense melts of semiflexible polymers using the bond-fluctuation model. The chosen Hamiltonian increases the chain stiffness upon cooling which in turn leads to glass-transition like freezing of the polymer mobility. Employing an efficient simulation algorithm, which is able to equilibrate the simulated systems to lower temperature than the Rouse-type algorithm showing the glassy freezing, we are able to observe an isotropic-nematic phase transition. This transition lies above the glass transition temperature one would extrapolate from the observed freezing behavior.
Monte Carlo simulations of the polymer glass transition: From the test of theories to material modeling
1997
We present results on the glass transition in polymer melts using Monte Carlo simulations of the bond fluctuation lattice model. There are two questions we address in this work. What is the temperature dependence of the entropy density in such a model polymer melt and how well is it described by theories like the Gibbs-DiMarzio theory of the glass transition? And to what degree is one able to map the Hamiltonian of such an abstract lattice model onto a specific polymer material and use it to model the large scale and long time properties of a realistic polymer melt?
Electronic structure of polysilanes: influence of substitution and conformation
1993
Abstract The valence effective Hamiltonian (VEH) quantum-chemical approach is used to investigate the electronic properties of polysilane. The valence band structure calculated for this fully saturated polymer is analyzed in terms of orbital contributions and compared to that of the closely related carbon polymer, polyethylene. The effects of alkyl substitution and silicon backbone conformation are studied by elucidating the modifications that these structural changes induce on the electronic valence band structure of all-trans unsubstituted polysilane. The VEH results predict a decrease of the band gap upon alkyl substitution and on going from helical to all-trans conformations.
Toward Understanding the Photochemistry of Photoactive Yellow Protein: A CASPT2/CASSCF and Quantum Theory of Atoms in Molecules Combined Study of a M…
2009
Photochemical processes that take place in biological molecules have become an increasingly important research topic for both experimentalists and theoreticians. In this work, we report the reaction mechanism of a model of the photoactive yellow protein (PYP) chromophore in vacuo. The results obtained here, using a strategy based on the simultaneous use of the minimum energy path concept and the quantum theory of atoms in molecules applied to this excited state process, suggest a possible way in which the protein could increase the efficiency of the reaction. The role played by other electronic states of the same and different spin multiplicities in the reaction process is also analyzed, wi…
The Nonlocal Correlation Density Functional VV10
2015
Abstract In this chapter, we review the most relevant attempts to merge the Vydrov and van Voorhis nonlocal density-dependent functional kernel (VV10) with modern density functionals to accurately describe van der Waals interactions with a reasonable computational cost. The chapter is organized by providing first an introduction of the relevance of van der Waals interactions and the difficulties of common density functionals to describe these forces. Second, the historical developments that eventually give rise to the most modern formulation of the nonlocal density functional VV10 are briefly addressed. Then, an overview of its technical formulation, adjustable parameters, and implementatio…
Measurement of the spin-dependent structure function g1(x) of the deuteron
1993
We report on the first measurement of the spin-dependent structure function g1d of the deuteron in the deep inelastic scattering of polarised muons off polarised deuterons, in the kinematical range 0.006<x<0.6, 1 GeV2<Q2<30 GeV2. The first moment, Γ1d=sh{phonetic}01 g1d dx=0.023±0.020 (stat.) ± 0.015 (syst.), is smaller than the prediction of the Ellis-Jaffe sum rules. Using earlier measurements of g1p, we infer the first moment of the spin-dependent neutron structure function g1n. The difference Γ1p-Γ1n=0.20 ±0.05 (stat.) ± 0.04 (syst.) agrees with the prediction of the Bjorken sum rule, Γ1p-Γ1n=0.191 ±0.002.
Effective charge from lattice QCD
2020
Using lattice configurations for quantum chromodynamics (QCD) generated with three domain-wall fermions at a physical pion mass, we obtain a parameter-free prediction of QCD's renormalisation-group-invariant process-independent effective charge, $\hat\alpha(k^2)$. Owing to the dynamical breaking of scale invariance, evident in the emergence of a gluon mass-scale, this coupling saturates at infrared momenta: $\hat\alpha(0)/\pi=0.97(4)$. Amongst other things: $\hat\alpha(k^2)$ is almost identical to the process-dependent (PD) effective charge defined via the Bjorken sum rule; and also that PD charge which, employed in the one-loop evolution equations, delivers agreement between pion parton di…
Dynamics and extraction of quantum discord in a multipartite open system
2011
We consider a multipartite system consisting of two noninteracting qubits each embedded in a single-mode leaky cavity, in turn connected to an external bosonic reservoir. Initially, we take the two qubits in an entangled state while the cavities and the reservoirs have zero photons. We investigate, in this six-partite quantum system, the transfer of quantum discord from the qubits to the cavities and reservoirs. We show that this transfer occurs also when the cavities are not entangled. Moreover, we discuss how quantum discord can be extracted from the cavities and transferred to distant systems by traveling leaking photons, using the input-output theory.