Improved Generator Coordinate Hartree Fock Research Articles

Accurate Gaussian basis sets for the ground state of the CS molecule

Sequences of increasing size atom centered basis sets of Gaussian-type functions for the ground state of the CS molecule are generated with the molecular improved generator coordinate Hartree-Fock (HF) method. At the HF level, total and orbital energies and electric dipole moment and, at the second-order Mφller-Plesset (MP2) level, correlation and dissociation energies and electric dipole moment were calculated and compared with the results obtained with other Gaussian basis sets reported in the literature. Considering our largest basis set, the HF energy is in error by 56.2 µhartree and the second order correlation energy corresponds to » 80% of an estimate of the limiting value. At the MP2 level, the dipole moment and the dissociation energy computed with our largest basis set are in good agreement with the corresponding experimental values. The CS molecule is considered a prototype for systems containing atoms from different rows of the periodic table.

Gaussian Basis Sets for Some Polyatomic Two‐Heavy‐Atom Hydrides

AbstractFor Abstract see ChemInform Abstract in Full Text.

Gaussian basis sets for CO2 molecule generated with the molecular improved generator coordinate Hartree?Fock method

The molecular improved generator coordinate Hartree–Fock (MIGCHF) method is used to generate increasing size atom-centered Gaussian basis sets for the CO2 molecule. From these basis sets total HF energies and second-order correlation energies were calculated and compared with results obtained with other approaches. Considering our largest basis set, the HF energy is in error by 98 μhartree and the second-order correlation energy corresponds to ∼95.6% of an estimate of the limiting value. The relevance of the present calculations is to show the accuracy that can be achieved in studies of small polyatomic molecules with the MIGCHF method.

Gaussian basis sets for low-lying excited states of neutral atoms with 2 ≤ Z ≤ 36

The improved generator coordinate Hartree–Fock method is used to generate Gaussian basis sets for low-lying excited states of neutral atoms from He (Z = 2) to Kr (Z = 36). Then, excitation energies and orbital energies of the outermost orbitals of each symmetry are calculated and compared with the corresponding values obtained with numerical Hartree–Fock calculations. Besides this, the basis sets for Be (3P) and F (2P) are contracted by a standard procedure and, then, enriched with polarization functions. From these basis sets, total energies, dissociation energy, and bond length for BeF are calculated and compared with results obtained with other basis sets and with experimental values. The sets for He–Kr are useful in constructing basis sets for molecular calculations. Key words: improved generator coordinate Hartree–Fock method, Gaussian basis sets, low-lying excited states, neutral atoms.

Accurate Gaussian basis sets for the H 2O molecule generated with the molecular improved generator coordinate Hartree–Fock method

The molecular improved generator coordinate Hartree–Fock (MIGCHF) method is used to generate accurate basis sets of primitive Gaussian-type functions for the H 2O molecule. Sequences of increasing size atom centered basis sets are employed to explore the accuracy that can be achieved with this method. Using the O(24s14p8d5f2g1h);H(22s9p5d2f1g) basis set, the HF and second-order electron correlation energies of the H 2O ground state at the experimental geometry are computed as −76.0674680 and −0.3491935 hartree, respectively. The HF energy is in error by 20 μhartree and the second-order correlation energy corresponds to 96.5% of an estimate of the limiting value. The relevance of the present calculations is to show the accuracy that can be achieved in studies of small polyatomic molecules with the MIGCHF method.

Highly accurate Gaussian basis sets for the atoms from H through Xe

AbstractAn improved generator coordinate Hartree–Fock (IGCHF) method is used to generate highly accurate Gaussian basis sets (GBSs) for the atoms from H (Z = 1) through Xe (Z = 54). In this method the Griffin–Hill–Wheeler–Hartree–Fock equations are integrated using the integral discretization technique. From these basis sets the ground‐state HF total energies are calculated and compared with the corresponding values obtained with GBSs of the same size, generated with the original generator coordinate Hartree–Fock method, and with a numerical HF method. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 190–193, 2003

Gaussian basis sets for polyatomic molecules containing first‐ and second‐row atoms

AbstractContracted Gaussian basis sets plus polarization functions generated from the improved generator coordinate Hartree‐Fock (HF) method are used to calculate some physical and chemical properties of the following molecules: CH4, NH3, H2O, SiH4, PH3, and H2S. Ground‐state HF total energies and, at the HF and second‐order Møller–Plesset levels, geometrical parameters, harmonic vibrational frequencies, and electric dipole moments are evaluated and compared with the corresponding experimental values and with those calculated with the 6‐311G** basis sets. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 144–148, 2003

An accurate Gaussian basis set for N 2, BF, and CO molecules

A molecular improved generator coordinate Hartree–Fock (HF) method is used to generate a highly accurate Gaussian basis set (GBS) for N 2, BF, and CO molecules. This basis set contains 26s15p8d5f primitive Gaussian-type functions on each center. Our ground state HF total energies are near the HF limits, and are better than those obtained with a larger universal GBS (UGBS) (30s15p15d15f) and with specific GBSs of the same size (26s18p10d7f) for each molecule. Our second-order Møller–Plesset energy corrections are also better than the corresponding ones calculated with the larger UGBS.

Improved generator coordinate Hartree-Fock method applied to generate Gaussian basis sets for the isoelectronic series of the atoms He to Ne

We have generated Gaussian basis sets (GBSs) for the neutral and the first 20 cations members of the isoelectronic series of each ground state atom from He to Ne with the improved generator coordinate Hartree–Fock (IGCHF) method. For all atomic species studied here, our total energy errors are smaller than those calculated by the original GCHF method using GBSs of the same sizes. The largest difference between our total energy results and those computed with a numerical Hartree–Fock approach is equal to 215 μhartree for Co17+. We also compare the ionization potentials obtained with the IGCHF with the corresponding experimental values. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 252–262, 2002

Highly accurate Gaussian basis sets for some 14‐electron diatomic systems*

AbstractA molecular improved generator coordinate Hartree–Fock (HF) method is used to generate highly accurate Gaussian basis sets for N2, BF, CO, NO+, and CN−. For these molecular systems, sequences of basis sets of atom‐centred Gaussian‐type functions are employed to explore the accuracy achieved with this method. Our ground state HF total energies are lower than the corresponding ones calculated with other basis sets of primitive Gaussian‐type functions reported in the literature. For the molecular systems here studied, the differences between the HF total energy results obtained with our largest basis sets and with a numerical HF method are equals to 38.2, 13.9, 33.0, 76.7, and 55.7 μhartree for N2, BF, CO, NO+, and CN−, respectively. We have also calculated the multipole electric moments and compare them with the corresponding experimental values and with results computed by other approaches. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002

Gaussian basis sets for the atoms from K through Xe

An improved generator coordinate Hartree-Fock (IGCHF) method is used to generate Gaussian basis sets for the atoms from K (Z = 19) through Xe (Z = 54). The Griffin-Hill-Wheeler-HF equations are integrated using the integral discretization technique. The ground state HF total energies obtained by us are compared with those calculated with the original GCHF method and with other approaches reported in the literature. The largest difference between our energy values and the corresponding ones computed with a numerical HF method is equal to 6.003 mhartree for Kr (Z = 36).Key words: improved generator coordinate Hartree-Fock method, Gaussian basis sets, total energies.

Improved generator coordinate Hartree-Fock method for molecular systems: application to H 2 , Li 2 and LiH

The improved generator coordinate Hartree–Fock (GCHF) method is extended to molecular systems. The Griffin–Hill–Wheeler–HF equations were solved by an integral discretization technique. The method is then implemented with the use of the GAMESS program and applied to the H2, Li2, and LiH molecules. For these molecules, sequences of basis sets of atom-centred Gaussian-type functions are employed to explore the accuracy achieved with our approach. For all systems studied, our ground-state HF total energies are better than those obtained with basis sets generated with the original GCHF method for molecules and larger even-tempered basis sets. For H2, Li2, and LiH, the differences between our best energies and the corresponding numerical HF results are about 2 × 10−2, 1, and 4 × 10−1 μhartree, respectively. The dipole, quadrupole, and octupole moments at the center of mass and electric field, the electric field gradient, the electrostatic potential, and the electron density at the nuclei were evaluated and compared with results reported in the literature.

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 Møller–Plesset (MP2), fourth-order Møller–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. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 15–23, 2000

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

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

Contraction of Gaussian basis sets for second-row diatomic molecules

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.

Accurate Gaussian basis sets for second-row atoms and ions generated with the improved generator coordinate Hartree–Fock method

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.

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

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.