Ab initio molecular calculations with pseudopotentials: calculations of double-zeta quality on BeH2, BH3, CH4, and C2H6

A new form of pseudopotential for applicaiton in ab initio molecular calculations is described. A method for determining pseudopotential parameters is suggested and pseudopotential parameters of double-zeta quality are presented for the first row atoms of the periodic table. The pseudopotential is especially well suited for incorporation into the floating-spherical-Gaussian-orbital (FSGO ) method, though it is not restricted to any particular method. Applications of the resulting pseudo-FSGO method to BeH₂, BH₃, CH₄, and C₂H₆ are presented.     

Ab initio molecular fragment calculations with pseudopotentials. Some fragments containing nitrogen and oxygen

Parameters for the OH (sp²) and NH₃ (planar, sp²) pseudopotential–FSGO molecular fragments have been established in this paper. Calculations for the molecules of formic acid, formaldehyde, and formamide show good agreement with experiment.     

A non-local pseudopotential in the FSGO model: Study of some organometallic systems

A non-local core pseudopotential has been used in the framework of floating spherical Gaussian orbital (FSGO ) model to study the equilibrium geometries and valence electronic structures of some organolithium and organoberyllium systems. The calculated equilibrium geometries, heats of hydrogenation, average electric polarizabilities, and magnetic susceptibilities are in good agreement with the results of the all-electron FSGO model calculations. Valence electron wave functions obtained here have been used to predict the valence electron Compton profiles (CP ) and electron momentum distributions (EMD ) of the systems studied. A good correlation has been shown among the peak height of the CP (J(0)), valence electron energy (E_v), and number of valence electrons (N_v).     

Electron momentum distributions and compton profiles of some alkali halides with FSGO model

The electron momentum distributions (EMD's) and Compton profiles (CP's) of LiF, LiCl, NaF and NaCI have been calculated using the floating spherical gaussian orbital (FSGO) model wavefunctions. The calculated FSGO Compton profiles are in good agreement with the available experimental data considering the simplicity of the model used. The calculated EMD and CP values in these systems are nearly equal to the sum of the contributions of respective cations and anions.     

Floating spherical Gaussian orbital model study of some hydrogen-bridged systems: LiBeH3, LiBH4, LiCH5, and BeBH5

The floating spherical Gaussian orbital (FSGO ) method has been used to study the equilibrium geometries and electronic structures of some hydrogen-bridged systems containing lithium, beryllium, boron, and carbon. The predicted geometries are in good agreement with other theoretical estimates. The binding energies for these hydrogen-bridged systems are estimated and discussed. The FSGO total energies (E_FSGO ), for all systems studied here, are found to be well correlated to nuclear–nuclear repulsion (V_nn) and nuclear–electron attraction (V_ne) terms by a relation of the type E_FSGO =\documentclass{article}\pagestyle{empty}\begin{document}$ {\textstyle{3 \over 7}} $\end{document} (2 V_nn + V_ne).     

A partial open shell FSGO calculation on the triplet methylene abstraction reaction with the hydrogen molecule: 3CH2 + H2 = CH3 + H

A partial open shell FSGO method is used to study the reaction path for the triplet methylene abstraction reaction with the hydrogen molecule, and the results obtained compare favourably with those from larger ab initio calculations.     

Calculation of molecular integrals for systems confined by hard spherical walls: Use of the single‐center expansion of floating spherical gaussians

Assuming a gaussian basis set representation of atomic and molecular wave functions, the single‐center expansion of off‐centered spherical gaussian orbitals is exploited to calculate the one and two‐electron integrals for multielectronic atoms and molecules confined within hard spherical walls. As a validating test, the ground‐state energy of a helium atom positioned off‐center in a spherical box is calculated by applying the simplest form of the floating spherical gaussian orbital (FSGO) scheme, i.e., the use of a primitive basis set consisting of a single FSGO per electron pair. Comparison with corresponding recent accurate calculations gives supporting evidence of the adequacy of the method for its application to more elaborate gaussian‐type basis set representations for confined atoms and molecules. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 271–278, 2001     

A floating spherical Gaussian orbital model of molecular structure

The FSGO model has been used to make ab initio calculations of the geometrical structures of borazane and diborane. Where experimental data are available there is good agreement between calculated and observed values.

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Zusammenfassung Für ab initio-Rechnungen zur geometrischen Struktur des Borazans und Diborans wurde das FSGO-Modell benutzt. Soweit experimentelle Werte vorhanden sind, stimmen die berechneten und beobachteten Werte gut überein.

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Résumé La méthode FSGO a été utilisée pour effectuer des calculs ab-initio sur les structures géométriques du borazane et du diborane. Un bon accord est obtenu entre les valeurs calculées et les valeurs expérimentales existantes.

     

On the use of model potentials with floating type of wavefunctions

The model potential method has been applied to an FSGO wavefunction in a manner suggested recently by Barthelat and Durand. Analysis of the theory of model potentials and exemplary calculations on first row atom hydrides indicate that the model potential method cannot in general be applied to the floating type of wavefunction.     

Explicitly correlated configuration interaction studies using spherical Gaussians. II. Exploratory studies on LiH

Ab initio self-consistent-field and configuration interaction studies have been carried out on the ground state of the LiH molecule at its equilibrium distance. Floating spherical Gaussian basis orbitals (FSGO ) were employed, along with spherical Gaussian correlation factors, using the procedure described in the preceding paper. A near-Hartree–Fock function was found using only 13 FSGO . Exploratory configuration interaction studies recovered approximately 73% of the inner shell correlation energy and approximately 56% of the total correlation energy with five configurations plus the Hartree–Fock configuration. These studies indicate that, by using spherical Gaussian correlation factors, direct introduction of interelectronic coordinates into trial wave functions can be accomplished for molecular systems. It was also shown that correlating configurations need not utilize the full Hartree–Fock basis, but may use substantially smaller bases and still recover correlation energy effectively. Finally, the results indicate that, in spite of their improper cusp behavior, FSGOS and spherical Gaussian correlation factors can be used for construction of high accuracy wave functions.     

A floating spherical gaussian orbital model of molecular structure. XII. Analysis of energy terms affecting the geometry of the water molecule

The energy terms arising in the water calculation by the FSGO method are analyzed as a function of the bond angle in order to gain insight into the reasons for the particular equilibrium configuration. The analysis is made in terms of symmetrically orthogonalized orbitals so as to exclude three- and four-orbital electron repulsion terms.     

Partitioning of FSGO charge distributions

A procedure for analyzing charge distributions of FSGO wavefunctions, by partitioning bonding electrons according to the location of the orbital centers, is proposed. Electron populations are given for singlet states of eighteen diatomic species, and are shown to be in excellent agreement with results obtained from virial partitioning of Hartree-Fock wavefunctions.     

Extended floating spherical gaussian basis sets for molecules. Generation procedure and result for H2O

A procedure is proposed to generate extended floating spherical gaussian orbital (FSGO) basis sets for molecular SCF calculations by projecting large basis set SCF results onto FSGOs. This replaces the need for repeated evaluation of energy integrals and SCF iterations for extensive non-linear optimizations of FSGOs.     

Floaing spherical gaussian orbital (FSGO) studies with a model potential: Some alkali halides

A gaussian based model potential is used in the framework of the FSGO approach to study the equilibrium geometries, force constants and charge distributions of some alkali halides (LiF, LiCl, NaF, NaCl, KF and KCl). The predicted results are in good agreement with the available experimental data and the results of other ab-initio studies.     

FSGO calculation of harmonic force fields of selected polyatomic hydrides

Harmonic force fields for several polyatomic hydrides of first-row atoms have been determined using the FSGO method and its extensions. The obtained results suggest that for larger polyatomic systems, the use of small, but completely optimised basis sets composed mainly of bond functions may be more economical than the conventional large basis set LCAO approach.     

Extended floating spherical Gaussian basis sets for molecules. Alternative correlating orbitals for molecular energy calculations

A procedure previously described for representing large basis SCF results in terms of a smaller floating spherical Gaussian orbital (FSGO) basis set is generalized to apply to the virtual orbitals from the SCF calculation. This provides a method for systematically reducing the dimensions of the virtual space or replacing the virtual orbitals with a simpler, compact basis set. The method is illustrated by application to Lill.     

FSGO point charge models—Their accuracy and extension to higher gaessians

An FSGO model of ethane demonstrates how currently used point charge models can give the wrong sign for the potential. The Hall point charge potential on the other hand is asymptotically accurate.An extension of the Hall point charge model to higher Gaussians is demonstrated. This extended model potential is shown to be of comparable accuracy to that of the spherical Gaussian model.