TURBOMOLE tools

All electron calculations were carried out with the DFT program suite Turbomole (152,153). The clusters were treated as open-shell systems in the unrestricted Kohn-Sham framework. For the calculations we used the Becke-Perdew exchange-correlation functional dubbed BP86 (154,155) and the hybrid B3LYP functional (156,157). For BP86 we invoked the resolution-of-the-iden-tity (RI) approximation as implemented in Turbomole. For all atoms included in our models we employed Ahlrichs valence triple-C TZVP basis set with polarization functions on all atoms (158). If not noted otherwise, initial guess orbitals were obtained by extended Hiickel theory. Local spin analyses were performed with our local Turbomole version, where either Lowdin (131) or Mulliken (132) pseudo-projection operators were employed. Broken-symmetry determinants were obtained with our restrained optimization tool (136). Pictures of molecular structures were created with Pymol (159). 

The main goal of the present work is to report the implementation of the explicitly-correlated coupled-cluster singles-and-doubles method (CCSD(F12)) in Turbomole. This tool is capable of very efficient calculating the CCSD energies at the basis set limit with relatively small orbital basis sets. The implementation works with RHF, UHF and ROHF reference wave functions, which means that it can treat both closed- and open-shell species. The formulation in terms of intermediate quantities and the application of density fitting techniques make this implementation quite unique. 

The thesis begins with Section 2, where a brief history about the explicitly correlated approaches is presented. This is followed by Section 3 with general remarks about standard and explicitly correlated coupled-cluster theories. In Section 4, the details about the CCSD(F12) model relevant to the implementation in TuRBOMOLE are presented. The usefulness of the developed tool is illustrated with the application to the problems that are of interest to general chemistry. A very accurate determination of the reactions barrier heights of two CH3+CH4 reactions has been carried out (Section 5) and the atomization energies of 106 medium-size and small molecules were computed and compared with available experimental thermochemical data (Section 6). The ionization potentials and electron affinities of the atoms H, C, N, O and F were obtained and an agreement with the experimental values of the order of a fraction of a meV was reached (Section 7). Within all applications, the CCSD(F12) calculation was only a part of the whole computational procedure. The contributions from various levels of theory were taken into account to provide the final result, that could be successfully compared to the experiment. 

TURBOMOLE consists of a. series of independent modules and their use is facilitated by various tools, mainly UNIX shellscripts. All modules use the general input file control which provides the necessary information either directly (keywords with options) or indirectly as cross reference to the corresponding file. The latter feature is conveniently (and as default) used for the documentation of MO vectors, gradients, etc., which typically constitute extended data sets. 

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