K.K. Sunil

Theoretical investigation of the a 3Σ+u, A 1Σ+u, c 3Σ+g, and C 1Σ+g potential energy curves of He2 and of He*(2 1S, 2 3S)+He scattering

Potential energy curves for the a 3Σ+u, A 1Σ+u, c 3Σ+g, and C 1Σ+g states of He2 are calculated using the MCSCF method. Comparison of the calculated dissociation energies and spectroscopic constants with the experimental values indicates that these are the most accurate theoretical curves reported to date for these states. The resulting curves are utilized to calculate the vibrational and rotational energy levels and to carry out He*(2 1S)+He(1 1S) and He*(2 3S)+He(1 1S) scattering calculations.

Theoretical study of the bonding in CuH and Cu2

The configuration interaction, Moller–Plesset perturbation theory, and coupled‐cluster procedures are utilized to determine the dissociation energies, vibrational frequencies, and bond lengths of CuH and Cu2. Good agreement is found between the theoretical and experimental values for these properties. Triple and quadruple excitations and the inclusion of diffuse f functions in the basis set are found to be important for quantitative predictions. A CCD+ST(CCD) approximation, in which the contributions of single and triple excitations are evaluated using the coupled‐cluster doubles (CCD) wave function, is found to give a value of De(Cu2) within 0.1 eV of the experimental value when a correction for a relativistic effects is included.

Theoretical study of the isomerization of cyanogen

Abstract Hartree-Fock and many-body perturbation theoretical calculations are used to determine the geometries and energies of NCCN ( 1 ), CNCN ( 2 ), and CNNC ( 3 ) as well as the transition state structures for interconversion among these three isomeric species. It is found that there is a reaction path with a relatively low (0.66 eV) barrier for conversion of 3 to 1 , consistent with the thermal instability of 3 .

Theoretical investigation of the structure and stability of AlCO and Al(CO)2 and their cations

Ab initio calculations are performed to determine the geometries and binding energies of AlCO and Al(CO)2 and their cations. The calculations reveal that the bonding between Al and the CO groups is due almost entirely to electron correlation, the second CO binds to Al much more strongly than the first, and the C-Al-C angle in both Al(CO)2 and its cation is 73–74°.

Theoretical study of the dipole moment, polarizability, and their derivatives for the CO molecule

Abstract Many-body perturbation theory and coupled-cluster theory are used to determine the dipole moment, polarizabilities, and their derivatives with respect to internuclear separation for the CO molecule. There are sizable errors in the dipole moment and its derivative when evaluated in the MP4(SDTQ ) approximation. Significantly improved results are obtained in the CCD + ST(CCD) approximation.

Application of the MC SCF method to the π → π* excitation energies of ethylene

Abstract The MC SCF method is employed to calculate the N → T and N → V π → π * vertical excitation energies of ethylene. To obtain accurate excitation energies it is found to be necessary to utilize an expanded valence space containing two π and two π * orbitals. Relatively small MC SCF calculations, allowing at most one-electron excitations from the sigma space, are found to yield excitation energies and spatial extents of the excited states in excellent agreement with the predictions of large multi-reference or iterative-natural-orbital CI calculations. These results show that within an MC SCF framework σ-σ correlation is unimportant for describing the π → π * processes. We also conclude that the neglect of the effects of unlinked cluster terms in some of the CI calculations may have introduced small, but important, errors in the excitation energies and predictions of the spatial extent of the V state.

Theoretical study of the 2Σu+ and 2Σg+ states of Li2− and Na2−

Abstract Ab initio calculations are performed to obtain potential energy curves for the X 1 Σ g + state of Li 2 and Na 2 and the X 2 Σ g + and A 2 Σ g + states of their anions. The A 2 Σ g + M 2 − curves are found to intersect the X 1 Σ g + M 2 curves at low energies and are expected to play a major role in the e − + M 2 → M − + M process.

Theoretical investigation of the low‐lying electronic states of Cu, Zn, and their ions

The ab initio SCF‐CI procedure is utilized to calculate the energies of the low‐energy excitation and ionization processes in Cu and Zn, as well as the electron affinity of Cu. Although tight f functions are required for describing d2 → f2 contributions to the correlation energy of individual states, diffuse f functions are found to be generally more important for describing the differential correlation in the electronic excitation and ionization processes.

Theoretical study of the NaClNaCl− ↔ ClNaNaCl− interconversion

Abstract Ab initio HF and MP2 procedures are used to characterize the NaClNaCl − and ClNaNaCl − forms of (NaCl) 2 − as well as the transition state for interconversion of the two ions. It is found that a barrier of about 0.27 eV exists for conversion of ClNaNaCl − to the more stable NaClNaCl −1 form of the anion.

Theoretical study of the 12A″ (X2II) State of N2 O+: implications for isotopic scrambling

Abstract Ab initio calculations suggest that the potential energy surface for the 12 A ″ state of N2O+ has a secondary minimum corresponding to a strongly bent structure. This structure is computed to lie below the A 2Σ + state energetically and therefore may be responsible for the isotopic scrambling observed in this energy region.