Search results for "Active space"

showing 3 items of 43 documents

Restricted and complete-active-space multiconfiguration linear response calculations of the polarizability of formamide and urea

1991

Abstract Using the polarized basis sets of Sadlej, we have carried out multiconfiguration linear response (MCLR) calculations of static and dynamic polarizabilities of water, carbon dioxide, formamide and urea. It is found that the polarized basis sets give a good description of the polarizabilities. The uncorrelates (self-consistent field) polarizabilities are in general 10% or more lower than the experimental values. The correlation as introduced in the complete-active-space (CAS) and restricted-active-space (RAS) MCLR calculations recovers the major part of this deviation.

chemistry.chemical_classificationFormamideField (physics)Basis (linear algebra)Triatomic moleculeGeneral Physics and AstronomyMolecular physicschemistry.chemical_compoundchemistryComputational chemistryPolarizabilityUreaPhysics::Atomic PhysicsComplete active spacePhysics::Chemical PhysicsPhysical and Theoretical ChemistryInorganic compoundChemical Physics Letters
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Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid

1997

The reaction mechanism for the decomposition of 2-chloropropionic acid in the gas phase to form hydrogen chloride, carbon monoxide, and acetaldehyde has been theoretically characterized. Analytical gradients have been used by means of AM1 and PM3 semiempirical procedures and ab initio methods at HF and DFT (BLYP) levels with the 6-31G** basis set. The correlation effects were also included by using the perturbational approach at the MP2 level with the 6-31G** and 6-31++G** basis sets and the variational approach at the CISD/6-31G** level and by means of MCSCF wave functions with a (6,6) complete active space and the 6-31G** basis set. The global potential energy surface has been studied, an…

chemistry.chemical_classificationchemistry.chemical_compoundchemistryComputational chemistryCarboxylic acidPotential energy surfaceAb initioElectronic structureComplete active spacePhysical and Theoretical ChemistryHydrogen chlorideBasis setCarbon monoxideThe Journal of Physical Chemistry A
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Theoretical Studies of the Electronic Spectra of Organic Molecules

1995

The complete active space (CAS) SCF method in conjunction with multiconfigurational second-order perturbation theory (CASPT2) has been used to study the electronic spectra of a large number of molecules. The wave functions and the transition properties are computed at the CASSCF level, while dynamic correlation contributions to the excitation energies are obtained through the perturbation treatment. The methods yield energies, which are accurate to at least 0.2 eV, except in a few cases, where the CASSCF reference function does not characterize the electronic state with sufficient accuracy. The applications comprise: the polyenes from ethene to octatetraene (cis- and trans-forms); a number …

chemistry.chemical_compoundChemistryStereochemistryOscillator strengthExcited stateMoleculeComplete active spaceRydberg stateGround stateMolecular physicsSpectral linePorphin
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