José Luis Pascual

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...

Ab initio model potential embedded cluster calculations including lattice relaxation and polarization: Local distortions on Mn2+‐doped CaF2

The ab initio model potentials initially developed as effective core potentials, have been proposed as embedding potentials in the field of embedded cluster calculations on impurities in ionic crystals [J. Chem. Phys. 89, 5739 (1988)] and, since then, efficiently used in the theoretical study of bulk and surface problems. These potentials bring into an ab initio cluster calculation, classical and quantum mechanical interactions with a frozen crystalline environment (Madelung, short‐range Coulomb, exchange, and orthogonality) at a reasonable cost. In this paper, we extend the ab initio model potential embedding method in order to include the effects of dipole polarization and site relaxation of lattice ions external to the cluster, which are represented by an empirical shell model. We apply the method to the ab initio calculation of local distortions around a Mn2+ impurity in CaF2 lattice in the ground state (6A1g) and two excited states (4T1g,4A1g) of the cubic MnF6−8 embedded cluster. In this material, x...

Ab initio model potential embedded‐cluster study of V2+‐doped fluoroperovskites: Effects of different hosts on the local distortion and electronic structure of 4T2g–4A2g laser levels

In this paper we present the results of ab initio model potential (AIMP) embedded‐cluster calculations on the ground 4A2g and excited 4T2g state levels of V2+‐doped KMgF3, KZnF3, KCdF3, and CsCaF3. Complete active space SCF (CASSCF) and averaged coupled‐pair functional (ACPF) calculations are performed on the (VF6)4− embedded cluster. The AIMP embedding potentials represent both static and relaxed/polarized lattice effects which are found to be an important refinement due to the large local distortions produced by the V2+ impurity. The calculated local distortions are found to be considerably large, but much smaller than expected in terms of the mismatch of ionic radius of the impurity and the substituted cation. The host dependency of the crystal field splitting, which was found to violate the simple ligand field R−5‐law in a wide family of V2+‐doped halide crystals, if R is the metal–ligand distance in the host, is also examined and is found to be quite close to the simple ligand field theory prediction...

Luminescence spectra of lead-doped NaCl, KCl and KBr

Abstract The luminescence spectra of lead-doped NaCl, KCl and KBr have been systematically investigated. Special attention has been paid to the effects of concentration and thermal history of the crystals. In the three systems, the emission spectra for A and C band excitation consists mainly of two well-defined emission bands whose energy separation is ∼0.7 eV. It has been concluded that none of the bands can be attributed to a single type of lead center but are both typical of Pb 2+ luminescence. In fact, their behavior can be correlated with that found for most monovalent ions and interpreted in a similar way. The excitation spectra for the two emissions have shown that the A-band is complex. One of the components appearing in very low doped and quenched samples is ascribed to dipoles, whereas additional side bands are attributed to complexes or small aggregates involving Pb 2+ ions.

Improved Embedding Ab Initio Model Potentials for Embedded Cluster Calculations

An improvement in the method of production of embedding ab initio model potentials (AIMP) for embedded cluster calculations in ionic solids is proposed and applied to the oxides CeAlO(3), CeO(2), and UO(2). The improvement affects the calculation of one of the AIMP components, the Pauli repulsion operator, which prevents the cluster electrons from collapsing onto the occupied orbitals of the host in embedded cluster calculations and, so, their over occupancy. The linear constants involved in such operator are proposed to be obtained in embedded cluster calculations in the perfect host, with the requirement that local structures calculated with working embedded clusters of relatively small size agree with those calculated with reference embedded clusters of much larger size.

Ab initio theoretical study of the structure and electronic spectra of Co 2 + in KZnF 3

In this paper we present the results of ab initio model potential embedded cluster calculations on

Ab initio model potential study of the optical absorption spectrum of Mn2+‐doped CaF2

({\mathrm{CoF}}_{6}{)}^{4\ensuremath{-}}

Theoretical study of the effects of F to Cl chemical substitution on the electronic structure and the luminescence properties of Cs2GeF6:Os4+ and Cs2ZrCl6:Os4+ materials

in the lattice of

On the electronic absorption spectrum of Cr4+ in Rb2CrF6

{\mathrm{KZnF}}_{3}

Ab initio model potential embedded-cluster calculation of the geometric structure of Tl+ monomer and dimer centers in KCl ☆

to model theoretically the different electronic spectra (absorption, emission and excited state absorption spectroscopies) of