guess_zero(matrix, spin_change=0, spin_block_symmetrisation='none')¶
Return an AmplitudeVector object filled with zeros, but where the symmetry has been properly set up to meet the specified requirements on the guesses.
matrix The matrix for which guesses are to be constructed spin_change The spin change to enforce in an excitation.
Typical values are 0 (singlet/triplet/any) and -1 (spin-flip).
Symmetrisation to enforce between equivalent spin blocks, which all yield the desired spin_change. E.g. if spin_change == 0, then both the alpha->alpha and beta->beta blocks of the singles part of the excitation vector achieve a spin change of 0. The symmetry specified with this parameter will then be imposed between the a-a and b-b blocks. Valid values are “none”, “symmetric” and “antisymmetric”, where “none” enforces no particular symmetry.