35.2 Wave function Ansätze
The so called ”ansatz” determines the definition of the explicitly correlated wave function. This is to
be distinguished from the various approximations that can be used to approximate the Hamiltonian matrix elements.
Generally, we use ansatz 3 (cf. I), for which the projector has the form
where is a one-electron projector for electron onto the occupied space, and projects
onto the virtual orbital space. In the case that domain approximations are used in local explicitly correlated
wave functions, the operators are replaced by operators that project just onto the
domain for the orbital pair .
In MOLPRO the following wave function ansätze can be used: