Search results for "Propadienylidene"
showing 2 items of 2 documents
Analytic first and second derivatives for the CCSDT-n (n = 1–3) models: a first step towards the efficient calculation of CCSDT properties
2000
Analytic first and second derivatives of the energy are implemented for closed-shell systems described by the CCSDT-n (n=1, 1b, 2 and 3) and CC3 electron correlation models. A detailed discussion of the computational requirements of these calculations is given, along with diagrammatic formulas for all relevant quantities. The method is applied to calculate the nuclear magnetic shielding of H2O, CO and N2O and the structure and properties of propadienylidene.
The equilibrium structure of propadienylidene
1999
Abstract A coupled-cluster study of the equilibrium geometry of propadienylidene (C3H2) is presented. Deviations between a recently reported experimental re structure and those computed at the CCSD(T)/cc-pVQZ and CCSD(T)/cc-pCVQZ levels are larger than expected. A closer analysis reveals that this discrepancy is due to inaccuracies in the cubic force field that was used to correct the measured rotational constants for vibrational effects. A satisfactory agreement between theory and experiment is obtained if the vibrational effects on the rotational constants are computed from harmonic and cubic force fields determined at either the CCSD(T)/cc-pVTZ and CCSD(T)/cc-pCVTZ levels. Revised values…