LCGTO calculations

Fig. 1. MEP contour maps calculated for the CO molecule using the SCF (la), MP2 (lb) and LCGTO-DF (Ic) methods. The contour levels and MEP minima are given in kcal/mol.

Similarly, expanding the KS potential in an LCAO expansion makes molecular density-functional calculations practical [9]. For metals and similar crystalline solids, it is best to expand the Kohn-Sham potential in momentum space via Fourier coefficients. For molecular solids various real-space method are under investigation. For molecules studied with the big, well-chosen Gaussian basis sets of quantum chemistry, it is undoubtedly best to expand the KS potential in linear-combination-of-Gaussian-type-orbital (LCGTO) form [10]. 

The geometry and selected vibrational frequencies of CUTiCHa have been calculated using the LCGTO-Xa method. The methyl group is found essentially undistorted, thus providing no indication for an agostic interaction. 

MuUiken charges reveals that the corresponding molecular orbitals (7a j and llb ) have some admixture of metal 4p states. The coupling with 4p states causes a transfer of the ligand s charge to originally unoccupied 4p orbitals of the metal. This "back donation" mechanism was first discovered in SW-Xa calculations (29) and is confirmed by the present LCGTO-LSDF study. 

In this paper, we presented explicit formulas for LCGTO-LSDF gradient calculations which require just the calculation of integral derivatives. Hence, the same highly efficient integral package can be applied. 

The reactivity of palladium and copper cluster models toward diazirine has been compared using the LCGTO-MCP-LSD method <1996SUS11> such calculations were performed to give an insight into the differential bond scission experimentally observed in the thermal decomposition of diazirine on palladium and copper surfaces. Stronger chemisorption was evident with palladium and furthermore, partial diazirine lowest-unoccupied molecular orbital (LUMO) occupation only occurred for the copper cluster model systems. The calculated N-N bond order was significantly decreased in the copper complexes of excited state diazirines, whereas palladium complexes remained unperturbed. 

In my group we have chosen to work with the LCGTO approach for a number of reasons, both historical and rational. First, the early work of Dunlap et showed that the method could provide remarkably accurate spectroscopic constants for the first-row diatomics. Comparisons with completely numerical calculations showed that the technical details could... 

Since a number of the results in the following sections were calculated with this approach, a brief description of the LCGTO method is presented here. The molecular orbitals are expanded by the usual LCAO expression ... 

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