E.V.R. de Castro

Improved generator coordinate Hartree–Fock method: application to first-row atoms

Abstract An improved generator coordinate Hartree–Fock (IGCHF) method is proposed as a useful generalization of the generator coordinate Hartree–Fock (GCHF) method. The IGCHF uses two or three sets of basis functions for each symmetry. The two and three sets of exponents are generated from two and three different arithmetic sequences, respectively. Ground state Hartree–Fock calculations for first-row atoms using optimized Gaussian basis sets of the same size, generated with the GCHF and IGCHF methods, are carried out to demonstrate the substantial improvement offered by the IGCHF method.

Accurate universal Gaussian basis set for hydrogen through lanthanum generated with the generator coordinate Hartree-Fock method

Abstract The generator coordinate Hartree-Fock method is applied to generate an accurate universal Gaussian basis set for the atoms H ( Z = 1) through La ( Z = 57). The Hartree-Fock energy results obtained with our universal Gaussian basis set are compared with numerical Hartree-Fock results and with Hartree-Fock energy results obtained by using optimized Gaussian basis sets. For the atoms B through Ca we have obtained, when compared to the corresponding numerical Hartree-Fock results, an energy value within the accuracy of 10 −5 –10 −4 E h , and for Sc through La this accuracy lies between 10 −4 and 10 −3 E h . The universal Gaussian basis set presented in this work is generated taking into account the sharing of exponential functions between all s, p and d atomic orbitals, i.e. the shell constraint.

ACCURATE GAUSSIAN BASIS SETS FOR SECOND-ROW ATOMS AND IONS GENERATED WITH THE IMPROVED GENERATOR COORDINATE HARTREE-FOCK METHOD

Abstract The improved generator coordinate Hartree–Fock (IGCHF) method is used to generate accurate Gaussian basis sets for the second-row neutral atoms, singly charged cations from Na + through Ar + , and stable singly charged anions from Na − through Cl − . For all second-row atoms and ions studied, the ground-state energies obtained with the triply-optimized Gaussian basis sets (generated with the IGCHF method) are always better than those obtained with the original generator coordinate Hartree–Fock method, and do not differ from the corresponding numerical Hartree–Fock results by more than 0.8 millihartree.

A UNIVERSAL GAUSSIAN BASIS SET FOR ATOMS CERIUM THROUGH LAWRENCIUM GENERATED WITH THE GENERATOR COORDINATE HARTREE-FOCK METHOD

The generator coordinate Hartree–Fock method is applied to generate a universal Gaussian basis set for the heavy atoms from Ce (Z=58) through Lr (Z=103). The Hartree–Fock energies obtained with our universal Gaussian basis set are compared with the new numerical Hartree–Fock results of Koga et al., when available, and with geometrical Gaussian basis sets results available in the literature. The universal Gaussian basis set presented here is generated taking into account the shell constraint (the sharing of exponential functions between all s, p, d, and f atomic orbitals), and can be used as starting basis set in ab initio relativistic Hartree–Fock–Roothaan calculations. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1565–1569, 1997

An improved generator coordinate Hartree-Fock method applied to the choice of contracted Gaussian basis sets for first-row diatomic molecules

Accurate Gaussian basis sets (18s for Li and Be and 20s11p for the atoms from B to Ne) for the first-row atoms, generated with an improved generator coordinate Hartree–Fock method, were contracted and enriched with polarization functions. These basis sets were tested for B2, C2, BeO, CN−, LiF, N2, CO, BF, NO+, O2, and F2. At the Hartree–Fock (HP), second-order Moller–Plesset (MP2), fourth-order Moller–Plesset (MP4), and density functional theory (DFT) levels, the dipole moments, bond lengths, and harmonic vibrational frequencies were studied, and at the MP2, MP4, and DFT levels, the dissociation energies were evaluated and compared with the corresponding experimental values and with values obtained using other contracted Gaussian basis sets and numerical HF calculations. For all diatomic molecules studied, the differences between our total energies, obtained with the largest contracted basis set [6s5p3d1f], and those calculated with the numerical HF methods were always less than 3.2 mhartree.

Contraction of Gaussian basis sets for second-row diatomic molecules

Abstract We have augmented the extended Gaussian basis sets (GBSs) (18s13p) previously generated for second-row atoms with an improved generator coordinate Hartree–Fock (HF) method up to (23s13p). These new extended basis sets are then contracted to [8s5p] and [8s6p] by a standard procedure; the latter, in combination with the previously contracted Gaussian basis set [6s4p] for the first-row atoms are enriched with polarization functions. These contracted basis sets are applied for the second-row diatomic molecules AlF, SiO, PN, SC, ClB and P2. The total and highest occupied molecular orbital HF energies are calculated and compared with the corresponding numerical HF (NHF) values. The dipole moments and bond lengths are calculated at the HF, MP2, MP4, CISD, and DFT levels, as well as the harmonic vibrational frequencies (HF, MP2, MP4, DFT levels) and the dissociation energies (MP2, MP4, DFT levels) and compared with the corresponding experimental values and with those obtained using other contracted GBSs and NHF calculations.

Development of method for monitoring of chloride release in the oil refining processes

ABSTRACT During oil refining, equipments are constantly exposed to the action of compounds such as salts, leading corrosion problems and to decrease in equipment service life. Soon, the growing search for productivity increasingly demand more strategies to monitor the processes and minimize costs. This article contributes to the methodology development to study the chlorides released during the oil distillation, in a similar process that occurs in refineries, enabling predict and minimize damage. Oils were evaluated with respect to chloride release during each stage of oil heating. Salinity mass balance were obtained as well as their respective chloride release percentage to each oil.