Non-empirical Pseudopotentials Research Articles

The molecular structure of bicyclo[1.1.0]tetraarsane from ab initio calculations using analytical gradients

The molecular structure of three different isomers of bicyclo[1.1.0]tetraarsane has been obtained by means of ab initio techniques including the use of non-empirical pseudo-potentials and analytical first derivatives of the total energy versus the nuclear coordinates. The results show unequivocally the existence of three different stable structures. The very small energy difference between the exo— exo and endo— exo is further evidence that these are in fact the two isomers found experimentally.

Calculation and analysis of the low-lying excited 3,1Σ + states of copper hydride

The lowest singlet and triplet Σ + potential-energy curves for the copper hydride molecule are investigated by means of valence-only CI calculations using non-empirical pseudopotentials derived from relativistic atomic calculations. Calculated spectroscopic constants are in good agreement with experimental data. The complex behaviour of the potential curves is discussed in terms of a diabatic description.

Theoretical evidence for two geometrical isomers of silver oxide (AgO2)

With use of nonempirical pseudopotentials and moderately large basis sets, SCF and CI calculations show that AgO/sub 2/ presents two nearly degenerate structures of C/sub 2 upsilon/ and C/sub s/ symmetry, respectively. The ground state of these structures is found to be a /sup 2/A/sub 2/ and a /sup 2/A''. While the SCF and the CI description are almost coincident, the effect of electron correlation on the geometrical parameters is found to be quite important.

Pseudopotential ab initio study of σ-complexes between metallic cations and allyl anion: application to propene catalytic partial oxidation mechanism

An ab initio MO study of the σ-complexes between the unsymmetrical conformation of the allyl anion and several metallic cations — Cu(II), Ni(II), Co(II), Fe(II), Zn(II), Mg(II) and Bi(III) — using non-empirical core pseudopotentials has been carried out in order to search for a correlation between the electronic properties of these complexes and the experimental selectivity of their oxides. p ]The stability of these complexes is related to the number of unpaired electrons. Cations showing great stability are present in selective catalysts. In these complexes the charge transfer from the allyl anion takes place without change of the electronic structure associated with its C-C bonds.

The chemical bonding in the lowest 5Σ −u and 1Σ +g states of Sc 2

The lowest 5Σ − u and 1Σ + g states of Sc 2 are calculated using a non-empirical HF Pseudopotential and a multi-reference single-and-double CI. The weak bond energy relative to the ground-state dissociation of the former state and the short equilibrium internuclear distance of the latter state are analyzed, and their bonding natures are explained.

The effect of electron correlation in the interaction of atomic hydrogen with Ben clusters 3≤n≤7

The Ben and Ben –H (3≤n≤7) systems have been studied at the SCF and CI levels using nonempirical pseudopotentials for the Be atoms. While the effect of electron correlation is of great importance in correctly describing the cluster properties, the interaction of atomic hydrogen with those clusters can be described quite accurately at the SCF level. From a quantitative viewpoint the distances to the surface and interaction energies are changed by about 0.03–0.05 Å and 6–8 kcal/mol, respectively. Vibrational frequencies for the perpendicular motion to the surface are affected more.

Vibrational frequencies of halogens adsorbed on Ag (100) based on ab initio cluster model calculations

Chemisorption of atomic halogens (Cl, Br, and I) on the Ag (100) surface is studied by means of a cluster model. Ab initio calculations using non-empirical pseudopotentials show that the main interactions arise from s and d silver atomic orbitals with the corresponding halogen p orbitals, in agreement with UPS measurements. Vibrational frequencies for the motion perpendicular to the surface are in good agreement with those obtained at low coverage by means of a molecular dipole moment model.

Molecular structure, vibrational frequencies and ionization potential of tin dihalides

Abstract The geometrical parameters for SnX 2 (X = Cl, Br, I) and SnX 2 + have been optimized at the SCF and Cl levels using non-empirical pseudopotentials and a basis set of double-zeta plus polarization quality. For the neutral molecules the geometrical parameters are in agreement with the experimental values, the difference being of only 2%. Vibrational frequencies and ionization potentials are also in agreement with experiment.

Electron affinities of Sc

The energies of the three lowest states of Sc are calculated and compared to the energy of the Sc ground state 3d 14s 2 ( 2D) using a non-empirical HF pseudopotential and the full CI. The result suggests that the 1D 0 (3d 14s 24p 1) state is lower than the 3D 0 (3d 14s 24p 1) state, both of them being lower than the 3d 24s 2 states. The calculated energy difference 0.16 eV is in good agreement with a recent experimental value 0.15 eV.

A pseudopotential study of the hydrogen bond in H2O·H2S, H2S·H2S and H2O·H2Se systems

Intermolecular potential energy curves for the hydrogen bonded systems H2O·H2S, H2O·H2Se and H2S·H2S were calculated with nonempirical pseudopotentials using optimized-in-molecules basis sets augmented by polarization functions. The H2O·H2O interaction energy curve has been also considered as a test case. The present results for H2O·H2S and H2S·H2S indicate much weaker intermolecular interactions than those found in previous ab initio calculations. The H2O·H2Se interaction was found to be quite similar to H2O·H2S.

Cu as a one-electron atom: Molecular structure and dissociation energy of CuOH

The molecular structure and dissociation energy of CuOH have been investigated using non-empirical pseudopotentials. Two kinds of pseudopotential have been used, either including or not the 3d 10 electrons of the Cu atom in the atomic core. At the SCF level and dealing explicitly with the 11 valence electrons of Cu, only about 60% of the experimental dissociation energy is recovered, while good agreement is found at the CI level. A difference of about 20 kcal/mol is found between the dissociation energies at the SCF level using the two kinds of pseudopotential. This difference is maintained at the CI level. Introduction of core-valence polarization and correlation effects overcomes the deficiency observed when only one electron is considered on the Cu atom.

Theoretical study of the AsN spectrum

The ground 1Σ g +, the lowest 1,3Π, 1,3Δ and 1,3Σ − excited states of the AsN molecule have been calculated using a double-zeta + polarization + diffuse basis set, large CI and non-empirical pseudopotentials. Agreement with experimental r c, ω c and transition energies is good. The calculated D c is 4.22 eV. The 1,3Σ − states are confirmed to be the perturbers of the 1,3Π states.

Ab initio molecular calculations including spin-orbit coupling. II. Molecular test on the InH molecule and application to the g states of the Ar 2* excimer

Ab initio CI relativistic calculations with non-empirical core pseudopotentials are achieved for the valence states of InH and the gerade Rydberg states of the Ar 2 * excimer using the quasi-degenerate perturbation theory in the Λ · Σ coupling scheme.

Copper atom as a one-electron system: Theoretical study of Cu2 and CuH

The ground state characteristics of Cu2 and CuH have been calculated by using explicitly only one electron for each copper atom. The remaining 28 electrons are kept as a frozen core, employing a nonempirical pseudopotential. A recently proposed perturbation method for core-valence polarization and correlation effects has been used to study, these molecules. The results are in fairly good agreement with the experimental values. Study of copper clusters with this method is suggested.

Theoretical study of the lowest potential curves of NaK

The lowest nine states of NaK have been calculated with large Cl using non-empirical pseudopotentials. A recently developed perturbation treatment of the core—valence polarization and correlation effects is applied. It greatly improves the calculated atomic energies of Na and K; and appears to be very important for energy curves of NaK, leading to an overall good agreement with the experimental results.

Cl investigations on the AlN molecule

The six lowest states, dissociating into the ( 2P) Al( 4S) N and ( 2P) Al( 2D) N atomic states, are calculated using a nonempirical pseudopotential for the representation of the atomic cores and an extensive CI. The ground state is assigned as 3Π, but the 1Σ + and 3Σ − minima are less than 0.5 eV higher. The results are compared with the few experimental data.

Non-empirical pseudo-potentials for molecular calculations

Our non-empirical pseudo-potential method is tested on the molecules ScH3, TiH3F, MnO4 -, Zn(CH3)2 and Pd(CO)4. The calculations are performed with the PSIBMOL algorithm, described in paper I (Mole...

Non-empirical pseudopotentials (PSIBMOL algorithm) for molecular calculations: The Rh2Cl2(CO)4 complex

The electronic structure of Rh2Cl2(CO)4 in the ground state is computed using the recently proposed PSIBMOL (Pseudo-potentials + IBMOL/H) formalism. The drawing of the total and differential isoelectronic contour maps supports the idea that there does not exist any rhodium-rhodium bond in such a binuclear complex, the origins of the preferred bent conformation having to be found elsewhere.

Theoretical calculation of the valence excited states of the AlH molecule

The ground and lowest excited state potential curves of the AlH molecule have been calculated in a double-zeta-plus polarization basis set of Gaussian type orbitals. The core electrons of the Al atom are taken into account through a nonempirical pseudopotential. Large scale CI’s are performed according to the CIPSI technique. The calculated transition energies, bond distances, and force constants are in good agreement with experiment for the observed excited states. Three new states with dissociative or long equilibrium distance potential curves have been identified.

Non-empirical pseudopotentials for molecular calculations

Improved three-parameter atomic pseudopotentials are theoretically determined from lithium to krypton. In view of further molecular calculations, accurate expressions are given for the pseudopotent...