Matches in DBpedia 2016-04 for { ?s ?p "Complete active space perturbation theory (CASPTn) is a four-component relativistic Hamiltonian based, multireference electron correlation method for computational investigation of molecular systems especially for those with heavy atoms such as, transition metals, lanthanides, and actinides. If the single reference methods and density functional theory cannot be used to describe electronic states of a system, CASPTn would be used instead. It would also be used for heavy atom systems which are not applicable with quasi-relativistic approaches.Although perbuation methods such as CASPTn is successful in describing the molecular systems, they still need Hartree-Fock wavefunction to provide a valid starting point. The perturbation theories cannot reach convergence if the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are degenerated. Therefore, CASPTn method is usually used with Multi-configurational self-consistent field method (MCSCF) to avoid near-degeneracy correlation effects."@en }
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- Complete_active_space_perturbation_theory abstract "Complete active space perturbation theory (CASPTn) is a four-component relativistic Hamiltonian based, multireference electron correlation method for computational investigation of molecular systems especially for those with heavy atoms such as, transition metals, lanthanides, and actinides. If the single reference methods and density functional theory cannot be used to describe electronic states of a system, CASPTn would be used instead. It would also be used for heavy atom systems which are not applicable with quasi-relativistic approaches.Although perbuation methods such as CASPTn is successful in describing the molecular systems, they still need Hartree-Fock wavefunction to provide a valid starting point. The perturbation theories cannot reach convergence if the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are degenerated. Therefore, CASPTn method is usually used with Multi-configurational self-consistent field method (MCSCF) to avoid near-degeneracy correlation effects.".