Explicitly correlated coupled cluster F12 theory with single and double excitations

Full explicitly correlated F12 coupled cluster theory with single and double excitations and with Slater-type geminal as a correlation factor is introduced and implemented within the standard approximation. The variant C that does not require integrals over the commutator between the kinetic operator and the correlation factor has been used. All the necessary integrals are analytically calculated. With variant C also, first results are reported for the correlation factor being the interelectronic distance coordinate, i.e., for original R12 method. Calculations have been performed for a set of eight molecules including CH2((1)A(1)), CH4, NH3, H2O, HF, CO, N-2, and F-2, as well as for the constituting atoms. Atomization energies are reported too. (C) 2008 American Institute of Physics.