Publications (43) View all
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Article: MOLCAS 7: The Next Generation.
Journal of Computational Chemistry. 01/2010; 31:224-247. -
Article: MOLCAS 7: the next generation.
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ABSTRACT: Some of the new unique features of the MOLCAS quantum chemistry package version 7 are presented in this report. In particular, the Cholesky decomposition method applied to some quantum chemical methods is described. This approach is used both in the context of a straight forward approximation of the two-electron integrals and in the generation of so-called auxiliary basis sets. The article describes how the method is implemented for most known wave functions models: self-consistent field, density functional theory, 2nd order perturbation theory, complete-active space self-consistent field multiconfigurational reference 2nd order perturbation theory, and coupled-cluster methods. The report further elaborates on the implementation of a restricted-active space self-consistent field reference function in conjunction with 2nd order perturbation theory. The average atomic natural orbital basis for relativistic calculations, covering the whole periodic table, are described and associated unique properties are demonstrated. Furthermore, the use of the arbitrary order Douglas-Kroll-Hess transformation for one-component relativistic calculations and its implementation are discussed. This section especially focuses on the implementation of the so-called picture-change-free atomic orbital property integrals. Moreover, the ElectroStatic Potential Fitted scheme, a version of a quantum mechanics/molecular mechanics hybrid method implemented in MOLCAS, is described and discussed. Finally, the report discusses the use of the MOLCAS package for advanced studies of photo chemical phenomena and the usefulness of the algorithms for constrained geometry optimization in MOLCAS in association with such studies.Journal of Computational Chemistry 07/2009; 31(1):224-47. · 4.58 Impact Factor -
Article: Role of electronic curve crossing of benzene S1 state in the photodissociation of aryl halides, effect of fluorination: RASSI‐SO MS‐CASPT2 study
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ABSTRACT: An ab initio study of the role of electronic curve crossing of benzene S1 state in the photo dissociation dynamics of the iodobenzene and effect of fluorination is presented. Two dissociative life times observed in iodobenzene is attributed to the coupled repulsive potential energy curves of the low-lying n−σ*, π−σ*, π−π* states. The direct channel is attributed to the alkyl like transition and the indirect channel is attributed to the mixing of the alkyl like transitions with the low lying benzene π−π* transitions. Fluorination of iodobenzene results in a substantial increase in the direct channel product. To analyze the possible role of electronic curve crossing of these transitions, potential energy curves of low-lying n−σ*, π−σ*, π−π* states were studied including spin-orbit and relativistic effects using the Restricted Active Space state interaction multistate complete active space perturbation theory (RASSI-MS-CASPT2) method. Crossing behavior of spin-free and spin-orbit potential energy curves was analyzed for the role of the benzene S1 state. Our results indicate the curve crossing region to be around 2.00–2.35 Å for both C6H5I and C6F5I. Analysis of effect of fluorination on the energies of states corresponding to benzene π−π* and n−σ* transitions suggests an increase in the energy of benzene π−π* states and a decrease in the energy of the states corresponding to n−σ* transitions. Increased spin-orbit gap, increased separation of the benzene S1(π−π*) state and n−σ* states in the region of curve crossing, lesser mixing of the π−π* and n−σ* states, an order of magnitude decrease in the transition strength to the benzene singlet transition all contributed to the observed substantial increase in the quantum yield of the direct channel product on fluorination of aryl halides. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009International Journal of Quantum Chemistry 03/2009; 109(9):1962 - 1974. · 1.36 Impact Factor -
Article: New relativistic atomic natural orbital basis sets for lanthanide atoms with applications to the Ce diatom and LuF3.
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ABSTRACT: New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are included as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.The Journal of Physical Chemistry A 11/2008; 112(45):11431-5. · 2.95 Impact Factor -
Article: Cholesky Decomposition-Based Multiconfiguration Second-Order Perturbation Theory (CD-CASPT2): Application to the Spin-State Energetics of CoIII(diiminato)(NPh)
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ABSTRACT: The electronic structure and low-lying electronic states of a CoIII(diiminato)(NPh) complex have been studied using multiconfigurational wave function theory (CASSCF/CASPT2). The results have been compared to those obtained with density functional theory. The best agreement with ab initio results is obtained with a modified B3LYP functional containing a reduced amount (15%) of Hartree–Fock exchange. A relativistic basis set with 869 functions has been employed in the most extensive ab initio calculations, where a Cholesky decomposition technique was used to overcome problems arising from the large size of the two-electron integral matrix. It is shown that this approximation reproduces results obtained with the full integral set to a high accuracy, thus opening the possibility to use this approach to perform multiconfigurational wave-function-based quantum chemistry on much larger systems relative to what has been possible until now.04/2008;
