6533b7d0fe1ef96bd125a1ea
RESEARCH PRODUCT
High excitations in coupled-cluster series: vibrational energy levels of ammonia
Mihály KállayPierre ValironLauri HalonenTimo RajamäkiJozef Nogasubject
010304 chemical physicsElectronic correlationChemistryBiophysics010402 general chemistryCondensed Matter Physics01 natural sciencesPotential energyFull configuration interaction0104 chemical sciencesCoupled clusterSaddle point0103 physical sciencesPotential energy surfacePhysical and Theoretical ChemistryAtomic physicsWave functionSeries expansionMolecular Biologydescription
The ammonia molecule containing large amplitude inversion motion is a revealing system in examining high-order correlation effects on potential energy surfaces. Correlation contributions to the equilibrium and saddle point geometries, inversion barrier height and vibrational energy levels, including inversion splittings, have been investigated. A six-dimensional Taylor-type series expansion of the Born–Oppenheimer potential energy surface, which is scaled to different levels of theory, is used to determine vibrational energy levels and inversion splittings variationally. The electronic energies are calculated by coupled-cluster methods, combining explicitly correlated R12 theory (which includes the interelectronic coordinate in the electronic wave function) with a conventional approach including excitations up to the pentuple level. Finally, the electronic correlation contribution is scaled to the full configuration interaction limit. Corrections due to relativistic and non-Born–Oppenheimer effects are al...
| year | journal | country | edition | language |
|---|---|---|---|---|
| 2004-11-10 | Molecular Physics |