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MOLCAS/OpenMolcas is an ab initio electronic structure program providing a large set of computational methods from Hartree–Fock and density functional theory to various implementations of multiconfigurational theory. This article provides a comprehensive overview of the main features of the code, specifically reviewing the use of the code in previously reported chemical applications as well as more recent applications including the calculation of magnetic properties from optimized density matrix renormalization group wave functions.

A b i n i t i o model potential study of local distortions around Cr+ and Cr3+ defects in fluoriteIn 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 CuCI~cluster (all-electron calculation) embedded in a NaCllattice which is represented by 118 model-potential ions and 604 point-charge ions. The calculation reveals that (i) the quantum interactions between the CuCI~ -cluster and the rest of the lattice play an important role in determining the Cu-Cl distance and (ii) a considerable local distortion around the Cu + impurity is predicted in which the CI-ions move towards the Cu + impurity about 0.1 A.These results are in qualitative agreement with recent EXAFS studies; however, the predicted distortion is smaller than the one suggested by the EXAFS measurements.

Electronic transitions in luminescent molecules or centers in crystals couple to vibrations. This results in broadening of absorption and emission bands, as well as in the occurence of a Stokes shift E Stokes . In principle, one can derive from E Stokes the Huang-Rhys parameter S, which describes the microscopic details of the vibrational coupling and can be related to the equilibrium position offset DQ e between the ground state and excited state. The commonly used textbook relations E Stokes = (2S À 1) ho and E Stokes = 2S ho are only approximately valid. In this paper we investigate how E Stokes is related to S, taking into account the effects of a finite temperature. We show that in different ranges of temperature, different approximate relations between E Stokes and S are appropriate. Moreover, we demonstrate that the difference between the barycenters of absorption and emission bands can be used to determine S in an unambiguous way.The position of the barycenter is, contrary to the Stokes shift, unaffected by temperature.

This pelper is dedicated to Professor Sigeru Huzinaga on the occasiotz of his 65th Dirthclc~yZOILA BARANDIAKAN and Lurs SEIJO. Can. J. Chem. 70, 409 (1992).A comprehensive tabulation of Cowan-Griffin relativistic n b irzitio core model potentials and valence basis sets corresponding to the Cowan-Griffin ab itzitio model potential method is presented. It includes those for the elements from Li (Z = 3) to La ( Z = 57), the alkaline M' and alkaline earth M" cations, and for the halogen X -anions. Molecular results are presented in order to test the potentials and basis sets and to estimatc the extent of the mass-velocity and Darwin relativistic effects considered within thc method, which lie within thc cxpectcd margins.Key

The a b i n i t i o model potential method. Second series transition metal elements The a b i n i t i o model potential method. First series transition metal elements In this paper we present the ab initio core model potential method, in which the Coulomb and exchange core operators J c 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 ofN 2 , P 2 , As 2 , Sb 2 , 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.

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,4d͔ core was chosen for Ce-Lu and a ͓Xe,4f ,5d͔ core was chosen for Th-Lr. Minimal (14s10p9d8 f )/͓2s1 p1d1 f ͔ and (14s10p11d9 f )/͓2s1 p1d1 f ͔ valence basis sets were, respectively, optimized for Ce-Lu and Th-Lr, and a ͓6s5 p5d4 f ͔ 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.

An ab initio theoretical study of the optical absorption spectrum of Ni 2ϩ -doped MgO has been conducted by means of calculations in a MgO-embedded ͑NiO 6 ) 10Ϫ 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 ͑NiO 6 ) 10Ϫ cluster. The spin-orbit calculations have been performed using the spin-orbit-CI WB-AIMP method ͓Chem. Phys. Lett. 147, 597 ͑1988͒; J. Chem. Phys. 102, 8078 ͑1995͔͒ 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 based on the use of spin-free-state shifting operators. It is shown that the unreasonable spin-orbit splittings obtained for MgO:Ni 2ϩ in spin-orbit-CI calculations correlating only 8 electrons become correct when the proposed extension is applied, so that the same CI space is used but energy corrections due to correlating up to 26 electrons are included. The results of the ligand field spectrum of MgO:Ni 2ϩ show good overall agreement with the experimental measurements and a reassignment of the observed E g (b 3 T 1g ) excited state is proposed and discussed.