Zoila Barandiarán

The ab initio model potential representation of the crystalline environment. Theoretical study of the local distortion on NaCl:Cu+

In this paper we formulate a model potential approach to take into account the crystalline environment within the Hartree–Fock–Roothaan formalism. The formulation is based on the assumption that the theory of separability of many‐electron systems may be applicable to the group of electrons within a reference cluster and the groups of electrons on a set of external lattice sites which, in turn, can be represented according to the ab initio model potential method. The characteristics of the model potentials permit to analyze the contributions to the cluster energies and wave functions of different environmental effects, such as point‐charge and charge‐density Coulomb interactions and quantum interactions (exchange and orthogonality). The formalism is applied to the SCF calculation on the ground state of the octahedaral CuCl5−6 cluster (all‐electron calculation) embedded in a NaCl lattice which is represented by 118 model‐potential ions and 604 point‐charge ions. The calculation reveals that (i) the quantum ...

The ab initio model potential method. Main group elements

In this paper we present the ab initio core model potential method, in which the Coulomb and exchange core operators Jc and Kc are represented as accurately as possible using adequate local and nonlocal potentials, and the valence basis set is optimized in atomic MP SCF calculations following the variational principle. Nonrelativistic model potential parameters and valence basis sets are presented for the main group elements from Li to Xe. The pilot SCF molecular calculations on the ground states of N2, P2, As2, Sb2, and CaO show a good agreement between all‐electron and model potential results, in particular the changes observed in molecular results due to improvements of the valence part of the all‐electron basis set are reproduced by the model potential calculations.

Bonding between CO and the MgO(001) surface: A modified picture

The interaction energy and equilibrium distance for adsorption of CO on a perfect MgO(001) surface has been calculated, using a cluster approach for representing the surface. The cluster size has been varied from one single Mg2+ ion up to Mg14O5. Ab initio model potentials (AIMP) were used to embed the explicitly described cluster while the rest of the crystal was taken to be point charges. The AIMP model potentials are shown to be a necessary and reliable improvement, compared with using only point charges as a model for the surrounding crystal. It is found that the electrostatic attraction and Pauli repulsion almost cancel each other and the small binding energy obtained is ascribed to dispersive forces. The interaction energy is calculated to be 0.07–0.09 eV (depending on which approach to basis set superposition errors corrections is taken); this is rather low in comparison with the experimental value of 0.3–0.4 eV.

Ab initio model potential calculations on the electronic spectrum of Ni2+ -doped MgO including correlation, spin–orbit and embedding effects

An ab initio theoretical study of the optical absorption spectrum of Ni2+‐doped MgO has been conducted by means of calculations in a MgO‐embedded (NiO6)10−cluster. The calculations include long‐ and short‐range embedding effects of electrostatic and quantum nature brought about by the MgO crystalline lattice, as well as electron correlation and spin–orbit effects within the (NiO6)10− cluster. The spin–orbit calculations have been performed using the spin–orbit‐CI WB‐AIMP method [Chem. Phys. Lett. 147, 597 (1988); J. Chem. Phys. 102, 8078 (1995)] which has been recently proposed and is applied here for the first time to the field of impurities in crystals. The WB‐AIMP method is extended in order to handle correlation effects which, being necessary to produce accurate energy differences between spin–free states, are not needed for the proper calculation of spin–orbit couplings. The extension of the WB‐AIMP method, which is also aimed at keeping the size of the spin–orbit‐CI within reasonable limits, is base...

Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX2 (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I)

The ground state equilibrium geometry of alkaline earth dihalides MX2 (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I) has been optimized at the Hartree–Fock (HF) level using the Cowan–Griffin relativistic ab initio model potential method and a uniformly good, extended, spd valence basis set. The results show that, according to the method, all magnesium dihalides and CaCl2, CaBr2, and CaI2 are linear, SrF2 and all barium dihalides are bent, and CaF2 and SrCl2, SrBr2, and SrI2 are quasilinear molecules. The alkaline earth (n−1)d orbitals are shown to be responsible for the bending of the heavier molecules while their (n−1)p orbitals contribute considerably to the final quantitative prediction of the apex angle and the relative stability of the bent structures. Relativistic effects are shown to be very small on the bond distances and vibrational frequencies; they are important on the size of the bending barrier of the bent molecules. The results obtained are compared to previous theoretical studies and provide some insig...

The abinitio model potential method. Second series transition metal elements

In this paper we present nonrelativistic and relativistic core ab initio model potentials (AIMPs) and valence basis sets for La and the third-series transition metal elements. The relativistic AIMPs are derived from atomic Cowan–Griffin calculations; they are made of a spin-free part and a one-electron spin-orbit operator according to Wood and Boring. The core potentials correspond to the 62-electron core [Cd,4f]. The valence basis sets are optimized and spin-orbit corrected. We present monitoring spin-free calculations on the atoms, singly ionized ions and monohydrides of the ten elements, which show a good performance overall. A spin-free-state-shifted spin-orbit-configuration interaction calculation on Pt, which uses empirical spin-free data and which is expected to be essentially free from spin-free deficiencies, points out that the quality of the spin-orbit operators is very good.

Ab initio model potential study of environmental effects on the Jahn–Teller parameters of Cu2+ and Ag2+ impurities in MgO, CaO, and SrO hosts

In this paper, the differential effects brought about by the MgO, CaO, and SrO family of hosts on the topology of the energy surface corresponding to the ground state of the clusters (CuO6)10− and (AgO6)10− along the a1g and eg,θ vibrational modes, are studied by means of the ab initio embedding model potential method (AIEMP) at the restricted open‐shell Hartree–Fock level. For all six defect crystals, the equilibrium geometries, Jahn–Teller energies, vibrational frequencies, and relative energies between D4h elongated and compressed structures (energy barriers) have been calculated using (a) two different definitions of the defect cluster, namely (MeO6)10− and (MeO6M6)2+ (Me=Cu, Ag; M=Mg, Ca, Sr), (b) two different cluster LCAO expansions (including or not impurity second neighbor components), and (c) relativistic Cowan–Griffin ab initio (core and environment) model potentials. The results show the importance of using basis set functions located at lattice sites next to the (CuO6)10− and (AgO6)10− cluste...

The abinitio model potential method. First series transition metal elements

In the a b i n i t i o core model potential method the Coulomb and exchange core operators are represented accurately and the valence basis set is the only component of the method which is optimized (following the variational principle) in an atomic valence restricted Hartree–Fock (RHF) calculation. In this paper we present the nonrelativistic Ar‐like and Mg‐like core model potentials and valence Gaussian basis sets for the first series transition metal elements. The pilot RHF molecular calculations on ScO, MnO, CuO, and ScS show that freezing the 3s orbital is safe all along the transition series but the same is true for the 3p orbital only towards the end of the series. A good agreement exists between the all‐electron and model potential results if the same type of valence part of the basis set is used: 0.01 A in R e and 25 cm− 1 in ν e .

The ab initio model potential method: Lanthanide and actinide elements

In this paper we present relativistic core ab initio model potentials based on atomic Cowan–Griffin calculations, together with Wood–Boring spin-orbit operators and optimized Gaussian valence basis sets, for the lanthanide elements Ce to Lu and for the actinide elements Th to Lr. This completes the chemically relevant part of the Periodic Table. A [Kr,4d] core was chosen for Ce–Lu and a [Xe,4f,5d] core was chosen for Th–Lr. Minimal (14s10p9d8f )/[2s1p1d1f] and (14s10p11d9f )/[2s1p1d1f] valence basis sets were, respectively, optimized for Ce–Lu and Th–Lr, and a [6s5p5d4f] contraction is recommended for all these 28 elements in molecular calculations. The atomic and molecular results show the same good quality already observed for the main-group elements and the transition metal elements.

Transferability of core potentials to f and d states of lanthanide and actinide ions

An analysis is made of the transferability of frozen core potentials of neutral lanthanide and actinide elements to 4f/5f and 5d/6d states of their respective 3+ and 4+ ions. A good description of the orbital spin—orbit coupling constants ζ4f/ζ5f and ζ5d/ζ6d of the Ln3+/An4+ ions and of the 4f → 5d/5f ζ 6d transition energies is achieved by using [Kr]/[Xe, 4f] cores. The corresponding relativistic core ab initio model potentials (AIMPs) based on Cowan—Griffin atomic calculations, together with optimized Gaussian valence basis sets, are produced for the lanthanide elements Ce to Lu and for the actinide elements Th to Lr. Results are given for the Ce3+ and Pa4+ free ions and in Ce3+-and Pr3+-doped Cs2NaYCl6 and Pa4+-and U4+-doped Cs2ZrCl6 materials.