pinecone/core-2020-05-10-deduplication huggingface dataset:
Spin-density-functional theory: some open problems and application to
  inhomogeneous Heisenberg models

Spin-density-functional theory (SDFT) is the most widely implemented and
applied formulation of density-functional theory. However, it is still finding
novel applications, and occasionally encounters unexpected problems. In this
paper we first briefly describe a few of the latter, related to issues such as
nonuniqueness, noncollinearity, and currents. In the main part we then turn to
an example of the former, namely SDFT for the Heisenberg model. It is shown
that time-honored concepts of Coulomb DFT, such as the local-density
approximation, can be applied to this (and other) model Hamiltonians, too, once
the concept of 'density' has been suitably reinterpreted. Local-density-type
approximations for the inhomogeneous Heisenberg model are constructed.
Numerical applications to finite-size and impurity systems demonstrate that DFT
is a computationally efficient and reasonably accurate alternative to
conventional methods of statistical mechanics for the Heisenberg model.Comment: 15 pages, 1 figure, 1 tabl
Interaction induced magnetic field asymmetry of nonlinear mesoscopic
  electrical transport

We demonstrate that the nonlinear I-V characteristics of a two probe
conductor is not an even function of magnetic field. While the conductance of a
two-probe conductor is even in magnetic field, we find that already the
contributions to the current which are second order in voltage, are in general
not even. This implies a departure from the Onsager microreversibility
principle already in the weakly nonlinear regime. Interestingly, the effect
that we find is due to the Coulomb interaction. A measurement of the magnetic
field asymmetry can be used to determine the effective interaction strength. As
a generic example, we discuss the I-V characteristics of a chaotic quantum dot.
The ensemble averaged I-V of such a cavity is linear: nonlinearities are due to
quantum interference. Consequently, phase-breaking reduces the asymmetry. We
support this statement with a calculation which treats inelastic scattering
with the help of a voltage probe.Comment: 45th Sanibel Symposium, submitted April 6, 200
Comment on "New Methods for Old Coulomb Few-Body Problems"

In this Comment on the above mentioned paper by F. E. Harris, A. M. Frolov,
and V. H. Smith, we briefly review our contributions to development of new
methods for solution of the Coulomb four-body problem. We show that our
research group, headed by Prof. T. K. Rebane, had a priority in using the fully
correlated exponential basis for variational calculations of four-body systems.
We also draw attention to the fact that our group subsequently implemented a
more advanced method, which uses highly efficient exponential-trigonometric
basis functions for solution of the same problem.Comment: Accepted by the International Journal of Quantum Chemistr
Electronic Fock space as associative superalgebra

New algebraic structure on electronic Fock space is studied in detail. This
structure is defined in terms of a certain multiplication of many electron wave
functions and has close interrelation with coupled cluster and similar
approaches. Its study clarifies and simplifies the mathematical backgrounds of
these approaches. And even more, it leads to many relations that would be very
difficult to derive using conventional technique. Formulas for action of the
creation-annihilation operators on products of state vectors are derived.
Explicit expressions for action of simplest particle-conserving products of the
creation-annihilation operators on powers of state vectors are given. General
scheme of parametrization of representable density operators of arbitrary order
is presented.Comment: LaTex, 26 pages; one equation added, misprints remove
On the Proof by Reductio ad Absurdum of the Hohenberg-Kohn Theorem for
  Ensembles of Fractionally Occupied States of Coulomb Systems

It is demonstrated that the original reductio ad absurdum proof of the
generalization of the Hohenberg-Kohn theorem for ensembles of fractionally
occupied states for isolated many-electron Coulomb systems with Coulomb-type
external potentials by Gross et al. [Phys. Rev. A 37, 2809 (1988)] is
self-contradictory since the to-be-refuted assumption (negation) regarding the
ensemble one-electron densities and the assumption about the external
potentials are logically incompatible to each other due to the Kato
electron-nuclear cusp theorem. It is however proved that the Kato theorem
itself provides a satisfactory proof of this theorem.Comment: 9 pages. Int. J. Quantum Chem., to appea
Geometrical Thermodynamic Field Theory

A manifestly covariant, coordinate independent reformulation of the
Thermodynamic Field Theory (TFT) is presented. The TFT is a covariant field
theory that describes the evolution of a thermodynamic system, extending the
near-equilibrium theory established by Prigogine in 1954. We introduce the {\it
Minimum Dissipation Principle}, which is conjectured to apply to any system
relaxing towards a steady-state. We also derive the thermodynamic field
equations, which in the case of alpha-alpha and beta-beta processes have
already appeared in the literature. In more general cases the equations are
notably simpler than those previously encountered and they are conjectured to
hold beyond the weak-field regime. Finally we derive the equations that
determine the steady-states as well as the critical values of the control
parameters beyond which a steady-state becomes unstable.Comment: 32 pages and 3 eps figure
Systematic calculation of molecular vibrational spectra through a
  complete Morse expansion

We propose an accurate and efficient method to compute vibrational spectra of
molecules, based on exact diagonalization of an algebraically calculated matrix
based on powers of Morse coordinate. The present work focuses on the 1D
potential of diatomic molecules: as typical examples, we apply this method to
the standard Lennard-Jones oscillator, and to the ab initio potential of the H2
molecule. Global cm-1 accuracy is exhibited through the H2 spectrum, obtained
through the diagonalization of a 30 x 30 matrix. This theory is at the root of
a new method to obtain globally accurate vibrational spectral data in the
context of the multi-dimensional potential of polyatomic molecules, at an
affordable computational cost.Comment: 30 pages including 6 figure
Convergence of an s-wave calculation of the He ground state

The Configuration Interaction (CI) method using a large Laguerre basis
restricted to l = 0 orbitals is applied to the calculation of the He ground
state. The maximum number of orbitals included was 60. The numerical evidence
suggests that the energy converges as Delta E^N approx A/N^(7/2) + B/N^(8/2) +
>... where N is the number of Laguerre basis functions. The electron-electron
delta-function expectation converges as Delta delta^N approx A/N^(5/2) +
B/N^(6/2) + ... and the variational limit for the l = 0 basis is estimated as
0.1557637174(2) a_0^3. It was seen that extrapolation of the energy to the
variational limit is dependent upon the basis dimension at which the exponent
in the Laguerre basis was optimized. In effect, it may be best to choose a
non-optimal exponent if one wishes to extrapolate to the variational limit. An
investigation of the Natural Orbital asymptotics revealed the energy converged
as Delta E^N approx A/N^6 + B/N^7 + ... while the electron-electron
delta-function expectation converged as Delta delta^N approx A/N^4 + B/N^5 +
>... . The asymptotics of expectation values other than the energy showed
fluctuations that depended on whether $N$ was even or odd.Comment: 12 pages, 10 figures, revtex format, submitted to Int.J.Quantum
  Chemistr
Convergence of the partial wave expansion of the He ground state

The Configuration Interaction (CI) method using a very large Laguerre orbital
basis is applied to the calculation of the He ground state. The largest
calculations included a minimum of 35 radial orbitals for each l ranging from 0
to 12 resulting in basis sets in excess of 400 orbitals. The convergence of the
energy and electron-electron delta-function with respect to J (the maximum
angular momenta of the orbitals included in the CI expansion) were investigated
in detail. Extrapolations to the limit of infinite in angular momentum using
expansions of the type Delta X_J = A_X/(J+1/2)^p + B_X/(J+1/2)^(p+1) + ...,
gave an energy accurate to 10^(-7) Hartree and a value of <delta> accurate to
about 0.5%. Improved estimates of <E> and <delta>, accurate to 10^(-8) Hartree
and 0.01% respectively, were obtained when extrapolations to an infinite radial
basis were done prior to the determination of the J -> infty limit. Round-off
errors were the main impediment to achieving even higher precision since
determination of the radial and angular limits required the manipulation of
very small energy and <delta> differences.Comment: 11 pages, 7 figures, revtex format, submitted to Int.J.Quantum
  Chemistr
A Table of Third and Fourth Order Feynman Diagrams of the Interacting
  Fermion Green's Function

The Feynman diagrams of the Green's function expansion of fermions
interacting with a non-relativistic 2-body interaction are displayed in first,
second and third order of the interaction as 2, 10 and 74 diagrams,
respectively. A name convention for the diagrams is proposed and then used to
tabulate the 706 diagrams of fourth order. The Hartree-Fock approximation
summons up 2, 8, 40 and 224 of them, respectively.Comment: 12 pages, 13 figures, 16 tables. Index typo in Sect III corrected.
  More lines in Table XV. Three more references. Expanded Summar
Time Evolution of the Neel State

A quasionedimentional spin chain (s=1/2) is considered as a lattice
consisting of two sublattices. The attention is paid to the states which are
pure spin states of the whole lattice and both sublattices, the value of the
sublattices' spins being maximum. It is shown that the Neel state can be
considered as a superposition of such states. The exact equation for this
superposition coefficients is developed.
  The possibility of the Neel state to be the eigenstate of a Hamiltonian is
discussed. Several model Hamiltonians are examined, the well known ones and few
novel Hamiltonians being considered. The time evolution of the Neel state in
different models is studied with the help of Fock-Krylov method.Comment: 10 pages, 5 figures. Submitted to IJQC. Typos corrected. Some results
  adde
Exact and quantum chemistry-like calculations in helium doped clusters: The He2Br2(X) example

7 pages, 2 figures, 2 tables.-- Issue title: "Proceedings from the Eleventh European Workshop on Quantum Systems in Chemistry and Physics", edited by Oleg Vasyutinskii, Jean Maruani, Piotr Piecuch, Gerardo Delgado-Barrio, Stephen Wilson.A quantum chemistry-like approach has been recently developed in our group to deal with HeN-BC doped helium clusters, where the BC dopant is a conventional diatomic molecule. The central idea is to consider the He atoms as electrons while the B and C atoms play the role of the nuclei in standard electronic structure calculations. The procedure provides energies and wavefunctions allowing to perform spectral simulations and, hence, making feasible to do proper comparisons with current experiments. However, because of the large difference of masses of He and electrons, and also to the replacement of Coulomb potentials by molecular interactions, it is worthy to assess to what extent the approximations involved in this model (decoupling of orbital angular momenta of the He atoms from the BC rotation and adiabatic separation of the BC stretch versus the He motions) lead to accurate results. In this work we address these issues on the 4He2-Br2(X) system, containing a couple of bosonic He atoms for which variational calculations can be performed.Funded by DGICYT Spanish grants (FIS2004-02461, CTQ2004-02415/BQU) and Spanish "Ramón y Cajal" Programme, Ministerio de Educación y Ciencia; Grant Number: PDRyC-2003-001015, PDRyC-2006-001017.Peer reviewe
Comparative study of unscreened and screened molecular static linear
  polarizability in the Hartree-Fock, hybrid-density functional, and density
  functional models

The sum-over-states (SOS) polarizabilities are calculated within the
approximate independent electron theories such as the Hartree-Fock
approximation and density functional models using the eigenvalues and orbitals
obtained from the self-consistent solution of single-particle equations. The
SOS polarizabilities are then compared with those calculated using the
finite-field method within three widely used single particle models: (1) the
Hartree-Fock (HF) method, (2) the three parameter hybrid generalized gradient
approximation (B3LYP), and (3) the parameter free generalized gradient
approximation due to Perdew-Burke-Ernzerhof (PBE). The comparison is carried
out for polarizabilities of 142 molecules calculated using the 6-311++G(d,p)
orbital basis at the geometries optimized at the B3LYP/6-311G** level. The
results show that the SOS method almost always overestimate the FF
polarizabilities in the PBE and B3LYP models. This trend is reversed in the HF
method however exception to the trend do exist. The mean absolute errors (MAE)
in the screened (FF) and unscreened (SOS) polarizability are 0.78 \AA$^3$ for
the HF method, 1.87 \AA$^3$ for the B3LYP, and 3.44 \AA$^3$ for the PBE-GGA.
The Hartree-Fock approximation predicts finite-field polarizabilities that are
smaller than those predicted by the PBE and B3LYP models. Finally, a simple
scheme is devised to obtain FF quality estimate of polarizability from those
obtained using the SOS method by exploiting the observed trends.Comment: 18 pages, ReVTex (International Journal of Quantum Chemistry, in
  press
Grid-based density functional calculation of many-electron systems

Exploratory variational pseudopotential density functional calculations are
performed for the electronic properties of many-electron systems in the 3D
cartesian coordinate grid (CCG). The atom-centered localized gaussian basis
set, electronic density and the two-body potentials are set up in the 3D cubic
box. The classical Hartree potential is calculated accurately and efficiently
through a Fourier convolution technique. As a first step, simple local density
functionals of homogeneous electron gas are used for the exchange-correlation
potential, while Hay-Wadt-type effective core potentials are employed to
eliminate the core electrons. No auxiliary basis set is invoked. Preliminary
illustrative calculations on total energies, individual energy components,
eigenvalues, potential energy curves, ionization energies, atomization energies
of a set of 12 molecules show excellent agreement with the corresponding
reference values of atom-centered grid as well as the grid-free calculation.
Results for 3 atoms are also given. Combination of CCG and the convolution
procedure used for classical Coulomb potential can provide reasonably accurate
and reliable results for many-electron systems.Comment: 17 pages, 1 figure, 6 tables, 34 reference
Bound state spectra of the 3D rational potential

We present bound state spectra of the 3D rational potential, $V(r)=r^2 +
\lambda r^2/(1+gr^2)$, $g>0$, by means of the generalized pseudospectral
method. All the thirty states corresponding to $n$=0--9 are considered for the
first time for a broad range of coupling parameters. These results surpass the
accuracy of \emph{all} other existing calculations published so far except the
finite-difference method, which yields similar accuracy as ours. Variation of
energies and radial distribution functions is followed with respect to the
interaction parameters. Special emphasis has been laid on \emph{higher}
excitations and \emph{negative} values of the interaction, where relatively
less work has been reported. The energy sequence is found to be different for
positive and negative interaction; numerically following a mirror-image
relationship \emph{usually}, if not always. Additionally, twenty energy
splittings arising from certain levels belonging to $n$=0--9 are systematically
studied as functions of the potential parameters. Several new states (including
the higher ones) are presented.Comment: 15 pages, 5 tables, 2 figures, 55 reference
The strange history of B functions or how theoretical chemists and
  mathematicians do (not) interact

$B$ functions are a class of relatively complicated exponentially decaying
basis functions. Since the molecular multicenter integrals of the much simpler
Slater-type functions are notoriously difficult, it is not at all obvious why
$B$ functions should offer any advantages. However, $B$ functions have Fourier
transforms of exceptional simplicity, which greatly simplifies many of their
molecular multicenter integrals. This article discusses the historical
development of $B$ functions from the perspective of the interaction between
mathematics and theoretical chemistry, which traditionally has not been very
good. Nevertheless, future progress in theoretical chemistry depends very much
on a fertile interaction with neighboring disciplines.Comment: 13 pages, LaTeX2e, 0 figures;. To appear in International Journal of
  Quantum Chemistry (Proceedings of the Conference Odyssey 2008 -- Mathematical
  and Computational Aspects of Molecular Electronic Structure Calculations
  Campus Saint-Jean, University of Alberta, Edmonton, Canada, June 2008
Range separation combined with the Overhauser model: Application to the
  H$_2$ molecule along the dissociation curve

The combination of density-functional theory with other approaches to the
many-electron problem through the separation of the electron-electron
interaction into a short-range and a long-range contribution (range separation)
is a successful strategy, which is raising more and more interest in recent
years. We focus here on a range-separated method in which only the short-range
correlation energy needs to be approximated, and we model it within the
"extended Overhauser approach". We consider the paradigmatic case of the H$_2$
molecule along the dissociation curve, finding encouraging results. By means of
very accurate variational wavefunctions, we also study how the effective
electron-electron interaction appearing in the Overhauser model should be in
order to yield the exact correlation energy for standard Kohn-Sham density
functional theory.Comment: submitted to Int. J. Quantum Chem., special issue dedicated to Prof.
  Hira
Total Cluster Energy Calculation of Lithium Ion Conductors by the DV-Xα Method

Recently several programs for the total cluster energy calculation have been developing in the DV-Xα method.   In this study, we have tried to calculate and compare total cluster energies of several diatomic molecules and model clusters of ionic conductors.   The total cluster energies of diatomic molecules have minimum near the equilibrium atomic distance of each molecules though the absolute value of the total cluster energy were slightly different each other.   In the case of the model cluster of the Li3N crystal, which is one of the typical Li ion conductors, we have obtained the energy change as a function of the site during the movement of a Li ion.   The energy change with the movement of the Li ion along the conduction path was considerably smaller than along other paths, consistent with the results by the band calculation and experiments.   The total cluster energy calculation method was enough useful for the discussion of the cluster energy
Fluorescence Spectra of Pr3+ Ions in Phosphate Materials Calculated by the DVME Method

Recently fluorescence spectra of rare-earth ions in oxide materials are very attractive for the applications of the optical amplification in optical fiber communications and white LED etc.   However, it has been difficult to calculate the fluorescence spectra of rare-earth ions by the first principle method.   In this study, we used the relativistic discrete-variational multi-electron (DVME) method, which is a configuration-interaction (CI) calculation program using the molecular orbitals obtained by the relativistic DV-Xα method.   We applied this method to the calculation of the fluorescence spectrum of the Pr3+ ions in phosphate materials.   The transition probability of the fluorescence was calculated in the same manner of the absorption.    The obtained theoretical fluorescence spectrum was good agreement with the experimental one, though the intensity of each peak was deeply dependent on the configuration of the surrounding structural units.   The results suggested that the DVME method was useful for the calculation of not only absorption but also fluorescence spectra of rare-earth ions in oxide materials
Structural alignment using the generalized Euclidean distance between
  conformations

The usual Euclidean distance may be generalized to extended objects such as
polymers or membranes. Here, this distance is used for the first time as a cost
function to align structures. We examined the alignment of extended strands to
idealized beta-hairpins of various sizes using several cost functions,
including RMSD, MRSD, and the minimal distance. We find that using minimal
distance as a cost function typically results in an aligned structure that is
globally different than that given by an RMSD-based alignmentComment: Accepted in IJQ
Semi-local density functional for the exchange-correlation energy of
  electrons in two dimensions

We present a practical and accurate density functional for the
exchange-correlation energy of electrons in two dimensions. The exchange part
is based on a recent two-dimensional generalized-gradient approximation derived
by considering the limits of small and large density gradients. The fully local
correlation part is constructed following the Colle-Salvetti scheme and a
Gaussian approximation for the pair density. The combination of these
expressions is shown to provide an efficient density functional to calculate
the total energies of two-dimensional electron systems such as semiconductor
quantum dots. Excellent performance of the functional with respect to
numerically exact reference data for quantum dots is demonstrated.Comment: to appear in Int. J. Quantum Chem. (2010
CHARMM force field parameterization of rosiglitazone

We develop a CHARMM-based interaction potential for rosiglitazone, a well-known selective ligand to the γ isoform of the peroxisome proliferator-activated receptor (PPARγ) and widely marketed antidiabetic drug of the thiazolidinedione (TZD) class. We derive partial atomic charges and dihedral torsion potentials for seven rotations in the molecule, for which there are no analogs available in CHARMM. The potential model is validated by performing a series of molecular dynamics simulations of rosiglitazone in neat water and of a fully solvated rosiglitazone-PPARγ complex. The structural and dynamical behavior of the complex is analyzed in comparison with available experimental data. The potential parameters derived here are readily transferable to a variety of pharmaceutically important TZD compounds.FAPESPCNP
Mini-bandstructure tailoring in pi-conjugated periodic block copolymers
  employing the envelope crystalline-orbital method

A strategy for the systematic design of polymeric superlattices with
tailor-made mini-bandgaps and carrier mini-effective masses is described and
computationally implemented by means of an envelope crystalline-orbital method,
which is a straightforward adaptation for molecules of the envelope-function
approximation widely used in solid-state physics. Such strategy relies on the
construction of pi-conjugated periodic block copolymers from well-characterized
parent polymers, in such a way that the above-mentioned electronic parameters
can be predicted from the lengths of the blocks. Illustrative calculations for
prototypical (PPP_x-PDA_y)_n superlattices demonstrate the plausibility of the
strategy and the advantages of the computational implementation employed.Comment: To appear in Int. J. Quant. Chem. (2010