TD-DFT is possible to calculate excited state that has different spin with the reference state. Here, we give some examples for such calculation.

Some important issues

Integral direct TDDFT

Since TDDFT is a capable to study medium to large molecules, so called integral-direct method is preferred in TD-DFT calculation. To apply integral-direct TDDFT, integral-direct SCF should be evoked that fully avoids to store electronic repulsive integrals in disk. Thus, molecules with several tens or even hundred of atoms are possible via TDDFT calcualiton.

Examples of spin-flip TDDFT

Here, we give some examples to perform spin-flip TDDFT calculation.

Spin-flip TDDFT to calculate triplet state of H2O molecule

We start from ground state of H2O. It is a close shell 1A1 state. We would like to calculate several triplet excited states using spin-flip TDDFT. Here is a input with comments. Notice: the words after # are comments. You may negelect them in your input. {{ $COMPASS Title

• H2O Molecule test run, cc-pvdz

Basis

• cc-pvdz

Geometry

• O 0.000000000 0.000000000 0.369372944 H 0.000000000 -0.783975899 -0.184686472 H 0.000000000 0.783975899 -0.184686472

End geometry Skeleton # You should not neglect this line. $END

$XUANYUAN Direct # this line and the following line is important. Direct SCF is required. Schwarz $END

$SCF RKS dft functional

• B3lyp

$END

# Spin flip up TDDFT calculation from RKS reference. $tddft imethod

• 1 # Starts from RKS calculation. 1 RKS, 2 UKS

isf

• 1 # require spin flip up calculation

idiag

• 1

itda

• 0 # TDDFT is evoked.

iexit

• 4 # For each irreps, 4 states are required.

$end

# Spin flip up TDA calculation from RKS reference. $tddft imethod

• 1 # Starts from RKS calculation. 1 RKS, 2 UKS

isf

• 1 # require spin flip up calculation

idiag

• 1

itda

• 1 # TDA is evoked.

iexit

• 4 # For each irreps, 4 states are required.

$end }}