4,307 research outputs found
Efficient Algorithm for Two-Center Coulomb and Exchange Integrals of Electronic Prolate Spheroidal Orbitals
We present a fast algorithm to calculate Coulomb/exchange integrals of
prolate spheroidal electronic orbitals, which are the exact solutions of the
single-electron, two-center Schr\"odinger equation for diatomic molecules. Our
approach employs Neumann's expansion of the Coulomb repulsion 1/|x-y|, solves
the resulting integrals symbolically in closed form and subsequently performs a
numeric Taylor expansion for efficiency. Thanks to the general form of the
integrals, the obtained coefficients are independent of the particular
wavefunctions and can thus be reused later.
Key features of our algorithm include complete avoidance of numeric
integration, drafting of the individual steps as fast matrix operations and
high accuracy due to the exponential convergence of the expansions.
Application to the diatomic molecules O2 and CO exemplifies the developed
methods, which can be relevant for a quantitative understanding of chemical
bonds in general.Comment: 27 pages, 9 figure
Adsorption of CO on a Platinum (111) surface - a study within a four-component relativistic density functional approach
We report on results of a theoretical study of the adsorption process of a
single carbon oxide molecule on a Platinum (111) surface. A four-component
relativistic density functional method was applied to account for a proper
description of the strong relativistic effects. A limited number of atoms in
the framework of a cluster approach is used to describe the surface. Different
adsorption sites are investigated. We found that CO is preferably adsorbed at
the top position.Comment: 23 Pages with 4 figure
QMCPACK: Advances in the development, efficiency, and application of auxiliary field and real-space variational and diffusion Quantum Monte Carlo
We review recent advances in the capabilities of the open source ab initio
Quantum Monte Carlo (QMC) package QMCPACK and the workflow tool Nexus used for
greater efficiency and reproducibility. The auxiliary field QMC (AFQMC)
implementation has been greatly expanded to include k-point symmetries,
tensor-hypercontraction, and accelerated graphical processing unit (GPU)
support. These scaling and memory reductions greatly increase the number of
orbitals that can practically be included in AFQMC calculations, increasing
accuracy. Advances in real space methods include techniques for accurate
computation of band gaps and for systematically improving the nodal surface of
ground state wavefunctions. Results of these calculations can be used to
validate application of more approximate electronic structure methods including
GW and density functional based techniques. To provide an improved foundation
for these calculations we utilize a new set of correlation-consistent effective
core potentials (pseudopotentials) that are more accurate than previous sets;
these can also be applied in quantum-chemical and other many-body applications,
not only QMC. These advances increase the efficiency, accuracy, and range of
properties that can be studied in both molecules and materials with QMC and
QMCPACK
Analytical calculation of pressure for confined atomic and molecular systems using the eXtreme-Pressure Polarizable Continuum Model
We show that the pressure acting on atoms and molecular systems within the
compression cavity of the eXtreme-Pressure Polarizable Continuum method can be
expressed in terms of the electron density of the systems and of the
Pauli-repulsion confining potential. The analytical expression holds for
spherical cavities as well as for cavities constructed from van der Waals
spheres of the constituting atoms of the molecular systems
Redox reactions with empirical potentials: Atomistic battery discharge simulations
Batteries are pivotal components in overcoming some of today's greatest
technological challenges. Yet to date there is no self-consistent atomistic
description of a complete battery. We take first steps toward modeling of a
battery as a whole microscopically. Our focus lies on phenomena occurring at
the electrode-electrolyte interface which are not easily studied with other
methods. We use the redox split-charge equilibration (redoxSQE) method that
assigns a discrete ionization state to each atom. Along with exchanging partial
charges across bonds, atoms can swap integer charges. With redoxSQE we study
the discharge behavior of a nano-battery, and demonstrate that this reproduces
the generic properties of a macroscopic battery qualitatively. Examples are the
dependence of the battery's capacity on temperature and discharge rate, as well
as performance degradation upon recharge.Comment: 14 pages, 10 figure
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