scf

scf

This option defines how to perform an SCF calculation

charge

Value An integer
Default 0

Define the total charge of the system.

spin2p1

Value An integer
Default 1 for even number of electrons
2 for odd number of electrons

Define the spin multiplicity of the system, i.e., 2 S + 1 , where S is the spin of the system. For example, to consider the singlet and triplet state, one should set spin2p1 to 1 and 3, respectively.

Note that spin2p1 can be either positive or negative. Both positive and negative spin2p1 represent the same spin multiplicity, but for a SCF wave function, alpha and beta orbitals will be occupied first, respectively. For example, for 11 electrons with spin2p1 being 1, there will be 6 alpha electrons and 5 beta electrons, like most quantum chemistry software does; but when spin2p1 is -1, there will be 5 alpha electrons and 6 beta electrons.

For odd number of electrons, a positive spin2p1 will first occupy alpha orbitals. If you want the beta orbitals to be occupied first, use a negative spin2p1. For example:

scf
  charge  0
  spin2p1 3
end
mol
  H 0. 0. 0.
  H 0. 0. 1.
end

In this case, the molecule will have 2 alpha electrons and 0 beta ones. For another input:

scf
  charge  0
  spin2p1 -3
end
mol
  H 0. 0. 0.
  H 0. 0. 1.
end

The molecule will have 2 beta electrons and 0 alpha ones.

type

Value R for restricted SCF (alpha and beta orbitals are restricted to be identical)
U for unrestricted SCF (alpha and beta orbitals are not necessarily identical)
Default R for singlet state
U for other states

For singlet states, both restricted and unrestricted SCF are available. Unrestricted SCF is very useful in treating spin polarized systems. For non-singlet states, only the unrestricted one can be used.

max_it

Value A non-negative integer
Default 128

Define the maximum number of SCF iteration.

Hint

You can set max_it to 0 to do a non-iterative calculation.

energy_cov

Value A real number
Default 1.E-6

The energy convergence threshold for SCF calculations.

density_cov

Value A real number
Default 1.E-8

The density matrix convergence threshold for SCF calculations.

Hint

The SCF calculation is determined to be convergent when both the energy and density convergence conditions are satisfied.

nodiis

Do not use direct inversion of the iterative subspace (DIIS) convergence acceleration algorithm.

print_MO

Print molecular orbital coefficients. Without this, only molecular orbital energies and occupancies are printed.

schwarz

Value A real number
Default 1.E-10

Define the Schwarz screening tolerance. All two-electron integral contributions below this tolerance will be discarded to speed up calculations. A positive real number is needed.

Warning

Do not set a too large value (like 1.E-5). It may leads to wrong results.

do_tso

Instead of doing ordinary SCF, do target state optimization (TSO) SCF. This is a powerful method for calculating excited and diabatic states. For theoretical details, please refer to:

Tutorials of using TSO-DFT can be found here: