scfguess

Define the type of initial guess. In most cases, atmden is recommended. mwfn, which reads a guess from a converged SCF, is also a good choice.
For target state optimization (TSO), symmetry-broken systems, or other special calculations, fragden can be used.

When the type is mwfn, Qbics will read the wave function using this mwfn file name.
When the type is tso, Qbics will save the reference wave function using this mwfn file name.

This defines atomic fragments for the initial guess. The format is:

frag num_electrons spin_multiplicity atom_range

There can be an arbitrary number of fragments, but all atoms must be included once and only once. They are only activated when type is fragden.

For example:

scfguess
   type fragden
   frag 0 1 1-9
   frag 0 -3 10-15 18
   frag -1 3 16 17
end

In this case, the molecule is decomposed into 3 fragments:

1. Atoms 1–9, with charge 0 and spin multiplicity 1;
2. Atoms 10–15 and 18, with charge 0 and spin multiplicity 3 (beta orbitals occupied first);
3. Atoms 16 and 17, with charge -1 and spin multiplicity 3.

For this guess, Qbics will perform 3 SCF calculations for all fragments, then superpose them as the initial guess for the SCF of the whole molecule. This can be used for ordinary, symmetry-broken, or TSO SCF.

This defines the orbitals for initial guess. The format is:

orb num_electrons spin_multiplicity  alpha_MO_indices : beta_MO_indices

There can be arbitrary number of orbital spaces, but all orbitals must be included once and only once. They are only activated when type is mwfn.

For example:

scfguess
   type mwfn
   file x.mwfn
   orb 12 1 1-6 : 1-6
   orb 2 1 7 : 8
   orb 0 1 8 : 7
end

In this case, the orbitals will be read from x.mwfn, and three orbital spaces are defined:

• Alpha orbitals 1,2,3,4,5,6 and beta orbitals 1,2,3,4,5,6, with 12 electrons and spin multiplicity 1.
• Alpha orbital 7 and beta orbital 8, with 2 electrons and spin multiplicity 1.
• Alpha orbital 8 and beta orbital 7, with 0 electrons and spin multiplicity 1 (since no electrons are assigned, the spin multiplicity can be arbitrary).

For this guess, Qbics will read orbitals from x.mwfn and assign occupation according to orb, then perform the subsequent ordinary or TSO SCF calculations.

Also, note that in this keyword, orbital order matters. For example,

scfguess
   type mwfn
   file x.mwfn
   orb 14 1 1-6 9 7 8 10-25 : 1-6 9 7 8 10-25
end

In this case, the 7 alpha and 7 beta electrons will occupy orbitals 1,2,3,4,5,6,9.