Search results for "Coupled cluster calculations"

showing 6 items of 16 documents

The CC3 model : An iterative coupled cluster approach including connected triples

1997

An alternative derivation of many-body perturbation theory (MBPT) has been given, where a coupled cluster parametrization is used for the wave function and the method of undetermined Lagrange multipliers is applied to set up a variational coupled cluster energy expression. In this variational formulation, the nth-order amplitudes determine the energy to order 2n+1 and the nth-order multipliers determine the energy to order 2n+2. We have developed an iterative approximate coupled cluster singles, doubles, and triples model CC3, where the triples amplitudes are correct through second order and the singles amplitudes are treated without approximations due to the unique role of singles as appro…

PhysicsMany-body problemsIterative methodIterative methodsGeneral Physics and AstronomyRelaxation (iterative method)Function (mathematics)Perturbation theoryFull configuration interactionUNESCO::FÍSICA::Química físicaPhysics and Astronomy (all)Coupled clusterCoupled cluster calculationsPerturbation theory ; Many-body problems ; Coupled cluster calculations ; Iterative methods ; Wave functions ; Variational techniquesComputational chemistryPerturbation theoryPhysical and Theoretical ChemistryPhysics::Chemical PhysicsWave function:FÍSICA::Química física [UNESCO]ParametrizationWave functionsMathematical physicsVariational techniques
researchProduct

Polarizability and optical rotation calculated from the approximate coupled cluster singles and doubles CC2 linear response theory using cholesky dec…

2004

A new implementation of the approximate coupled cluster singles and doubles CC2 linear response model using Cholesky decomposition of the two-electron integrals is presented. Significantly reducing storage demands and computational effort without sacrificing accuracy compared to the conventional model, the algorithm is well suited for large-scale applications. Extensive basis set convergence studies are presented for the static and frequency-dependent electric dipole polarizability of benzene and C60, and for the optical rotation of CNOFH2 and (−)-trans-cyclooctene (TCO). The origin-dependence of the optical rotation is calculated and shown to persist for CC2 even at basis set convergence. …

PolarisabilityChemistryUNESCO::FÍSICAGeneral Physics and AstronomyComputational physicsDipolePhysics and Astronomy (all)Coupled clusterCoupled cluster calculationsFullerene compoundsOptical rotation ; Coupled cluster calculations ; Organic compounds ; Polarisability ; Fullerene compoundsComputational chemistryPolarizability:FÍSICA [UNESCO]Convergence (routing)Organic compoundsOptical rotationPhysical and Theoretical ChemistryLinear response theoryOptical rotationBasis setCholesky decomposition
researchProduct

Rovibrational structure of the Ar–CO complex based on a novel three-dimensional ab initio potential

2002

The first three-dimensional ab initio intermolecular potential energy surface of the Ar–CO van der Waals complex is calculated using the coupled cluster singles and doubles including connected triples model and the augmented correlation-consistent polarized valence quadruple zeta (aug-cc-pVQZ) basis set extended with a (3s3p2d1f1g) set of midbond functions. The three-dimensional surface is averaged over the three lowest vibrational states of CO. Rovibrational energies are calculated up to 50 cm−1 above the ground state, thus enabling comprehensive comparison between theory and available experimental data as well as providing detailed guidance for future spectroscopic investigations of highe…

Potential Energy SurfacesCoupled Cluster CalculationsAb initioGeneral Physics and AstronomyPhysics and Astronomy (all)symbols.namesakeAb initio quantum chemistry methodsQuasimoleculesPhysics::Atomic and Molecular ClustersVibrational StatesPhysics::Atomic PhysicsPhysics::Chemical PhysicsPhysical and Theoretical ChemistryArgon:FÍSICA::Química física [UNESCO]Rotational-Vibrational StatesBasis setValence (chemistry)ChemistryRotational–vibrational spectroscopyCarbon CompoundsUNESCO::FÍSICA::Química físicaCoupled clustersymbolsArgon ; Carbon Compounds ; Quasimolecules ; Rotational-Vibrational States ; Potential Energy Surfaces ; Ab Initio Calculations ; Intermolecular Mechanics ; Coupled Cluster Calculations ; Vibrational StatesIntermolecular Mechanicsvan der Waals forceAtomic physicsGround stateAb Initio Calculations
researchProduct

Study of the benzene⋅N2 intermolecular potential-energy surface

2003

The intermolecular potential-energy surface pertaining to the interaction between benzene and N2 is investigated theoretically and experimentally. Accurate intermolecular interaction energies are evaluated for the benzene–N2 van der Waals complex using the coupled cluster singles and doubles including connected triples [CCSD(T)] method and the aug-cc-pVDZ basis set extended with a set of 3s3p2d1f1g midbond functions. After fitting the energies to an analytic function, the intermolecular Schrödinger equation is solved to yield energies, rotational constants, and Raman-scattering coefficients for the lowest intermolecular levels of several benzene–N2 isotopomers. Experimentally, intermolecula…

Potential Energy SurfacesCoupled Cluster CalculationsNitrogenBinding energyGeneral Physics and AstronomyPotential Energy Functionssymbols.namesakePhysics and Astronomy (all)IsomerismQuasimoleculesRotational IsomerismPhysics::Atomic and Molecular ClustersQuantum-mechanical explanation of intermolecular interactionsRotational StatesPhysical and Theoretical ChemistryPhysics::Chemical Physics:FÍSICA::Química física [UNESCO]Basis setSchrodinger EquationChemistryOrganic CompoundsIsotope EffectsIntermolecular forceStimulated Raman ScatteringUNESCO::FÍSICA::Química físicaCoupled clustersymbolsAtomic physicsvan der Waals forceOrganic Compounds ; Nitrogen ; Quasimolecules ; Potential Energy Surfaces ; Potential Energy Functions ; Coupled Cluster Calculations ; Rotational States ; Isomerism ; Isotope Effects ; Stimulated Raman Scattering ; Rotational Isomerism ; Schrodinger EquationRaman spectroscopyRaman scattering
researchProduct

Computational and experimental investigation of intermolecular states and forces in the benzene-helium van der Waals complex

2003

A study of the intermolecular potential-energy surface (IPS) and the intermolecular states of the perprotonated and perdeuterated benzene–He complex is reported. From a fit to ab initio data computed within the coupled cluster singles and doubles including connected triples model for 280 interaction geometries, an analytic IPS including two- to four-body atom–atom terms is obtained. This IPS, and two other Lennard-Jones atom–atom surfaces from the literature, are each employed in dynamically exact (within the rigid-monomer approximation) calculations of J = 0 intermolecular states of the isotopomers. Rotational constants and Raman-scattering coefficients for intermolecular vibrational trans…

Potential Energy SurfacesCoupled Cluster CalculationsRaman SpectraHelium Neutral AtomsOrganic Compounds ; Helium Neutral Atoms ; Intermolecular Mechanics ; Quasimolecules ; Potential Energy Surfaces ; Ab Initio Calculations ; Coupled Cluster Calculations ; Lennard-Jones Potential ; Isotope Effects ; Isomerism ; Rotational States ; Raman SpectraAb initioGeneral Physics and AstronomyIsotopomerssymbols.namesakePhysics and Astronomy (all)IsomerismAb initio quantum chemistry methodsQuasimoleculesKinetic isotope effectPhysics::Atomic and Molecular ClustersRotational StatesPhysics::Atomic PhysicsLennard-Jones PotentialPhysics::Chemical PhysicsPhysical and Theoretical Chemistry:FÍSICA::Química física [UNESCO]ChemistryOrganic CompoundsIsotope EffectsIntermolecular forceUNESCO::FÍSICA::Química físicaCoupled clusterLennard-Jones potentialsymbolsIntermolecular MechanicsAtomic physicsvan der Waals forceAb Initio Calculations
researchProduct

A theoretical study of the low-lying excited states of thieno[3,4-b]pyrazine

2009

The low-lying electronic excited states of thieno[3,4-b]pyrazine have been studied using the multiconfigurational second-order perturbation CASPT2 theory with extended atomic natural orbital basis sets. The CASPT2 results allow for a full interpretation of the electronic absorption and emission spectra and provide valuable information for the rationalization of the experimental data. The nature, position, and intensity of the spectral bands have been analyzed in detail. A preliminary comparative study of the ground-state geometry of thieno[3,4-b]pyrazine has been performed at the coupled cluster single and doubles and density functional theory levels using a variety of correlation-consisten…

PyrazineOrganic compounds perturbation theoryUNESCO::FÍSICAGeneral Physics and AstronomySpectral bandsRydberg statesFluorescenceGround statesCoupled cluster calculations ; Density functional theory ; Fluorescence ; Ground states ; Organic compounds perturbation theory ; Rydberg stateschemistry.chemical_compoundCoupled clusterchemistryCoupled cluster calculations:FÍSICA [UNESCO]Excited stateDensity functional theoryMoietyDensity functional theoryEmission spectrumPhysical and Theoretical ChemistryAtomic physicsGround state
researchProduct