Ota Bludsky

Bound and low-lying quasi-bound rotation-vibration energy levels of the ground and first excited electronic states of HeH2+

Abstract Adiabatic potential energy surfaces are calculated for the ground and first excited electronic states of HeH2+ including their respective lowest dissociation limits: HeH 2 + ( X 2 A ′ )→ He ( 1 S )+ H 2 + ( X 2 Σ g + ) and HeH 2 + ( A 2 A ′ )→ He + ( 2 S )+ H 2 ( X 1 Σ g + ) . Using the Sutcliffe–Tennyson Hamiltonian for triatomic molecules, the energies of the rotation–vibration bound states are determined variationally and the energy positions and widths of low-lying quasi-bound resonance states are obtained applying the stabilization method. For the excited electronic state a number of resonances are predicted which have considerably long lifetimes and can therefore be expected to be important for a detailed description of the chemical reactivity of the HeH2+ ion. The positions of these resonance states are shown to coincide closely with the eigenvalues of an approximate Hamiltonian derived when applying the concept of the Born–Oppenheimer adiabatic separation to the nuclear vibrational motions with different energy contents.

An ab initio quartic force field and the fundamental frequencies ofo-benzyne

Abstract The ab initio SCF, MCSCF and MP2 molecular energies, gradients and Hessians have been evaluated at 33 points for the ground electronic state of theo-benzyne molecule. The corresponding potential energy surfaces have been fitted to obtain a quartic force field from which the fundamental frequencies have been determined using second-order perturbation theory. Theoretical predictions reproduce the majority of the experimental data to a degree of agreement which allows a complete assignment of all the fundamental frequencies ofo-benzyne.

A Computationally Feasible DFT/CCSD(T) Correction Scheme for the Description of Weakly Interacting Systems

A computationally feasible DFT/CCSD(T) correction scheme is proposed for precise calculations (close to the CCSD(T) accuracy) of weakly interacting molecular clusters. This approach formally falls within the DFTD class of methods (empirically corrected DFT methods), however, there are several important differences between the DFT/CCSD(T) scheme proposed here and a standard DFTD approach: (i) it is parameter free, (ii) it does not use any damping functions, and (iii) the error of DFT is assumed to be anisotropic in general. In addition, the proposed DFT/CCSD(T) correction scheme allows the analysis of assumptions commonly used in the DFTD calculations. Applica- tion of this method on the ethylene-benzene and benzene-benzene complexes leads to the conclusion that interaction ener- gies obtained with the DFT/CCSD(T) correction scheme can be obtained with a near reference level accuracy with an er- ror not exceeding 0.1 kcal/mol. A proper choice of a reference set is shown to be more important than the anisotropy of the DFT/CCSD(T) correction.