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., , where 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.
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.
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.
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: