Knowledge Bank

Vector Method ab initio calculations of several of the low lying electronic states of $H2O$ will be presented, together with the major concepts of the Vector Method. Very large determinantal CI wavefunctions are easily generated by the method, which avoids the formation of the Hamiltonian matrix. Various basis sets have been used to study the contributions from different levels of excitation relative, to the SCF term. For the single-zeta basis (+ Rydberg) the inclusion of single through quadruple excitations has been found to give energies nearly identical to the full CI result. Comparisons with standard methods will be discussed.