scfguess

This option defines the initial guess of SCF calculations.

type

Value	hcore Will use the eigenvectors of the core matrix as initial guess. Usually, its performance is very bad
	atmden Will use the superposition of converged densities of all atoms in the system as initial guess. It is recommended for most cases
	fragden Will use the superposition of converged densities of fragments assigned by you as initial guess. This can be used for TSO or treating symmetry-broken systems
	mwfn Will read a wave function from a MWFN file as initial guess
	tso Will use a reference state (assigned with frag) to perform TSO calculation (assigned with orb). This is only used for TSO calculations
Default	atmden

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, or other special calculations, fragden can be used.

file

Value	A file name
Default	job name + .mwfn

When type is mwfn, Qbics will read wave function with using mwfn file name.

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

frag

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

frag num_electrons spin_multiplicity atom_range

There can be 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) atom 1,2,3,4,5,6,7,8,9, with charge 0 and spin multiplicity 1; (2) atom 10,11,12,13,14,15,18, with charge 0 and spin multiplicity 3 (beta orbitals occupied first); (3) atom 16,17, 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.

Hint

The total charge of fragments does not have to be the same as the total system.

Hint

Please refer to the keyword do_tso in scf for more details about TSO, when you want to use frag.

orb

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 3 orbital spaces are defined: (1) alpha orbital 1,2,3,4,5,6 and beta orbital 1,2,3,4,5,6, with 12 electron and spin multiplicity 1; (2) alpha orbital 7 and beta orbital 8, with 2 electrons and spin multiplicity 1; (3) alpha orbital 8 and beta orbital 7 with 0 electron and spin multiplicity 1 (since no electrons in this orbital space, actually spin multiplicity can be arbitrary).

For this guess, Qbics will read orbitals from x.mwfn and assign occupation according to orb, then do the following 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 orbital 1,2,3,4,5,6,9.

Hint

Please refer to the keyword do_tso in scf for more details about TSO, when you want to use orb.