7.3.6 Reading or generating start orbitals

Subrouine get_guess is the most general routine for reading orbitals. It can also convert orbitals from different basis dimensions, or generate a starting guess. For many purposes it may be simpler to use subroutine get_orb.

c-----------------------------------------------------------------------
      subroutine get_guess(orb,eig,op,irec,ifil,typedef,ntype,ibasdif,
     >                     icase,type,ipri,string)
c-----------------------------------------------------------------------
      implicit double precision (a-h,o-z)
      character*(*) typedef(ntype),type,string
      dimension orb(*),eig(*),op(*)

Input parameters:

irec

Default record for reading orbitals. Depending on the value of icase (see below), this or the record read by a previous guess_inp call will be used.

ifil

Default file for reading orbitals.

op

An operator (triangular, symmmetry 1) used for making virtual orbitals (typically h or f). This is only used for icase$\gt 1$.

typedef

Default orbital type(s) to be searched, e.g., NATURAL, CANONICAL, LOCAL. Whether these are used depends on the value of icase (see below). blank means any orbitals.

ntype

Number of types given.

ibasdif

If nonzero, allow start from different basis dimension.

icase

icase=-1: Use defaults passed to this routine only, i.e., don't use any data from guess_inp
icase=0: All input from guess_inp must be obeyed strictly, no defaults used.
icase=1: All input from guess_inp must be obeyed strictly if given. Otherwise the defaults irec,ifil,typedef are used.
icase=2: If input orbitals from guess_inp cannot be found, use the defaults passed to this routine.
icase=3: If nothing found, make eigenvectors of op.
For icase.ge.2, orbitals are orthogonalized.
For icase.le.1, eig and op are unused. Also no orthonromalization!

ipri

If non-zero, print info about orbitals (one line)

string

A string printed before 'orbitals', e.g. 'Molecular'

Output:

orb

Orbital vectors.

eig

Orbital energies (only available if iset_eig.gt.0).

type

Orbital type found.