Michel Dupuis

General atomic and molecular electronic structure system

A description of the ab initio quantum chemistry package GAMESS is presented. Chemical systems containing atoms through radon can be treated with wave functions ranging from the simplest closed‐shell case up to a general MCSCF case, permitting calculations at the necessary level of sophistication. Emphasis is given to novel features of the program. The parallelization strategy used in the RHF, ROHF, UHF, and GVB sections of the program is described, and detailed speecup results are given. Parallel calculations can be run on ordinary workstations as well as dedicated parallel machines.

Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation

Two major energy-related problems confront the world in the next 50 years. First, increased worldwide competition for gradually depleting fossil fuel reserves (derived from past photosynthesis) will lead to higher costs, both monetarily and politically. Second, atmospheric CO_2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atmospheric CO2.1 Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.

Evaluation of molecular integrals over Gaussian basis functions

This paper is concerned with the efficient computation of the ubiquitous electron repulsion integral in molecular quantum mechanics. Differences and similarities in organization of existing Gaussian integral programs are discussed, and a new strategy is developed. An analysis based on the theory of orthogonal polynomials yields a general formula for basis functions of arbitrarily high angular momentum. (ηiηj∥ηkηl) = Σα=1,nIx(uα) Iy(uα) I*z(uα) By computing a large block of integrals concurrently, the same I factors may be used for many different integrals. This method is computationally simple and numerically well behaved. It has been incorporated into a new molecular SCF program HONDO. Preliminary tests indicate that it is competitive with existing methods especially for highly angularly dependent functions.

High performance computational chemistry: An overview of NWChem a distributed parallel application☆

NWChem is the software package for computational chemistry on massively parallel computing systems developed by the High Performance Computational Chemistry Group for the Environmental Molecular Sciences Laboratory. The software provides a variety of modules for quantum mechanical and classical mechanical simulation. This article describes the design and some implementation details of the overall NWChem architecture. The architecture facilitates rapid development and portability of fully distributed application modules. We also delineate some of the functionality within NWChem and show performance of a few of the modules within NWChem.

Ab initio analytic polarizability, first and second hyperpolarizabilities of large conjugated organic molecules: Applications to polyenes C4H6 to C22H24

The static dipole polarizability and second hyperpolarizability tensors are calculated for polyene systems via ab initio coupled‐perturbed Hartree–Fock theory. The effect of basis set augmentation on the calculated properties is explored for C4H6 and example basis sets are used to calculate the polarizability and second hyperpolarizability for the longer polyenes: C6H8, C8H10, C10H12, C12H14, C14H16,C16H18, C18H20, C20H22, C22H24. Results for the finite polyenes are extrapolated to predict the unit‐cell polarizability and second hyperpolarizability of infinite polyacetylene. The working equations which take advantage of the 2n+1 theorem of perturbation theory for calculating up to the second hyperpolarizability are given, and their implementation is briefly discussed. In particular it is shown that the implementation is readily amenable to parallel processing.

Molecular symmetry. II. Gradient of electronic energy with respect to nuclear coordinates

Symmetry methods employed in the HONDO ab initio polyatomic SCF program are extended to the analytic computation of energy gradients. Validity of the Hellmann–Feynman theorem is not assumed, i.e., all two‐electron contributions to the gradient are included explicitly. The method is geared to the efficient computation of entire blocks of two‐electron integrals. Just one of a set of symmetrically related blocks must be computed. The gradient contribution from each unique block is multiplied by q4, the number of equivalent blocks, and added into a ’’skeleton gradient vector,’’ all other blocks are simply omitted. After processing molecular integrals, the true gradient vector is generated by projecting the symmetric component out of the skeleton vector. The analysis is based on Eqs. (26) and (33) which are valid for many variational wavefunctions including restricted closed shell and unrestricted open shell self‐consistent field functions. We also extend the use of translational symmetry proposed previously b...

Revisiting small clusters of water molecules

Abstract The geometries and relative energies of small clusters of water molecules, (H 2 O) n with 4 ⩽ n ⩽ 8, are reported. For each value of n we have considered the conformations corresponding to the lowest-energy minimum and those in nearby relative minima. Thus we report on six tetramers, four pentamers, six hexanlers, four heptamers, and eigth octamers. The geometrical conformations have been obtained using the Metropolis Monte Carlo method as a minimization technique, where the interaction energy is computed with the MCY potential plus three- and four-body corrections previously discussed. All the reported structures for a given cluster size are found to be close in energy. For the lowest conformation the geometry was optimized with ab initio SCF computations using energy gradients. Our results are compared with previous theoretical studies. We discuss the convergence of the interaction potential for liquid water when expressed in terms of a many-body series expansion.

Numerical integration using rys polynomials

Abstract We define and discuss the properties of manifolds of polynomials J n ( t , x ) and R n ( t , x ), called Rys polynomials, which are orthonormal with respect to the weighting factor exp(− xt 2 ) on a finite interval of t . Numerical quadrature based on Rys polynomials provides an alternative approach to the computation of integrals commonly encountered in molecular quantum mechanics. This gives rise to a curve fitting problem for the roots and quadrature weights as a function of the x parameter. We have used Chebyshev approximation for small x and an asymptotic expansion for large x . A modified Christoffel-Darboux equation applicable to Rys polynomials is derived and used to obtain alternative formulas for Rys quadrature weight factors.

Charge transport in metal oxides: A theoretical study of hematite α-Fe2O3

Transport of conduction electrons and holes through the lattice of α-Fe2O3 (hematite) is modeled as a valence alternation of iron cations using ab initio electronic structure calculations and electron transfer theory. Experimental studies have shown that the conductivity along the (001) basal plane is four orders of magnitude larger than the conductivity along the [001] direction. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e., the reorganization energy and the electronic coupling matrix element that enter Marcus’ theory. The calculation of the electronic coupling followed the generalized Mulliken–Hush approach using the complete active space self-consistent field method. Our findings demonstrate an approximately three orders of magnitude anisotropy in both electron and hole mobility between directions perpendicular and parallel to the c axis, in good accord with experimental data. The anisotropy ...

Nonlinear optical properties of p-nitroaniline : an ab initio time-dependent coupled perturbed Hartree-Fock study

For p‐nitroaniline the ab initio method with a double‐zeta basis set which includes semidiffuse polarization functions has been used to calculate the dipole moment μ, frequency‐dependent linear polarizability α, and nonlinear hyperpolarizabilities β and γ using the time‐dependent coupled perturbed Hartree–Fock approach. The computation procedure used here yields information on the dispersion behavior of all the tensor components of polarizability and various hyperpolarizability terms. The largest dispersion effect is observed for the diagonal components of the polarizability and hyperpolarizability tensors along the long in‐plane axis. The magnitudes of the various hyperpolarizability terms which describe the various second‐order nonlinear processes show the following trend: β(−2ω;ω,ω) ≳β(0;ω,−ω)=β(−ω;0,ω) ≳β(0;0,0), with β(−2ω;ω,ω) exhibiting the largest frequency dispersion. The various second hyperpolarizability terms which describe the various third‐order nonlinear optical processes show the following trend: γ(−3ω;ω,ω,ω) ≳γ(−2ω;0,ω,ω) ≳γ(−ω;ω,−ω,ω) ≳γ(−ω;0,0,ω) ≊ γ(0;0,ω,−ω) ≳γ(0;0,0,0). Again γ(−3ω;ω,ω,ω) shows the largest dispersion effect.The results of existing semiempirical calculations on p‐nitroaniline are compared with that of the present ab initio calculation, and the problem due to the arbitrary parametrization procedure adopted in the past for semiempirical calculation is discussed. The computed values of the first resonance energy, the dipole moment, and the polarizability are in good agreement with the respective values experimentally observed, within the spread of the existing experimental data. In contrast, the computed β and γ values are considerably smaller than the respective experimentally determined values. We attribute this discrepancy to two sources. First, in the theoretical calculation electron correlation has been neglected, and the basis set used, although large, may not still be adequate. Second, there is a considerable spread in the reported experimental values for a given nonlinear coefficient making any comparison between the theory and the experiment difficult.For p‐nitroaniline the ab initio method with a double‐zeta basis set which includes semidiffuse polarization functions has been used to calculate the dipole moment μ, frequency‐dependent linear polarizability α, and nonlinear hyperpolarizabilities β and γ using the time‐dependent coupled perturbed Hartree–Fock approach. The computation procedure used here yields information on the dispersion behavior of all the tensor components of polarizability and various hyperpolarizability terms. The largest dispersion effect is observed for the diagonal components of the polarizability and hyperpolarizability tensors along the long in‐plane axis. The magnitudes of the various hyperpolarizability terms which describe the various second‐order nonlinear processes show the following trend: β(−2ω;ω,ω) ≳β(0;ω,−ω)=β(−ω;0,ω) ≳β(0;0,0), with β(−2ω;ω,ω) exhibiting the largest frequency dispersion. The various second hyperpolarizability terms which describe the various third‐order nonlinear optical processes show the following...