# 9.7.2 Job Control and Examples

In order to perform non-adiabatic coupling calculations, the $derivative_coupling section must be given: $derivative_coupling
<one line comment>
i, j, k, ...
$end  Nonadiabatic couplings will then be computed between all pairs of the states $i,j,k,\ldots$; use “0” to request the HF or DFT reference state, “1” for the first excited state, etc. CALC_NAC Determines whether we are calculating non-adiabatic couplings. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE Calculate non-adiabatic couplings. FALSE Do not calculate non-adiabatic couplings. RECOMMENDATION: None. CIS_DER_NUMSTATE Determines among how many states we calculate non-adiabatic couplings. These states must be specified in the$derivative_coupling section.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0 Do not calculate non-adiabatic couplings. $n$ Calculate $n(n-1)/2$ pairs of non-adiabatic couplings.
RECOMMENDATION:
None.

Determines whether to include full quadratic response contributions for TDDFT.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
TRUE Include full quadratic response contributions for TDDFT. FALSE Use pseudo-wave function approach.
RECOMMENDATION:
The pseudo-wave function approach is usually accurate enough and is free of accidental singularities. Consult Refs. 1101 and 717 for additional guidance.

Example 9.15  Nonadiabatic couplings among the lowest five singlet states of ethylene, computed at the TD-B3LYP level using the pseudo-wave function approach.

$molecule 0 1 C 1.85082356 -1.78953123 0.00000000 H 2.38603593 -2.71605577 0.00000000 H 0.78082359 -1.78977646 0.00000000 C 2.52815456 -0.61573833 0.00000000 H 1.99294220 0.31078621 0.00000000 H 3.59815453 -0.61549310 0.00000000$end

$rem CIS_N_ROOTS 4 CIS_TRIPLETS false SET_ITER 50 CIS_DER_NUMSTATE 5 CALC_NAC true EXCHANGE b3lyp BASIS 6-31G*$end

$derivative_coupling 0 is the reference state 0 1 2 3 4$end


Example 9.16  Nonadiabatic couplings between $S_{0}$ and $S_{1}$ states of ethylene using BH&HLYP and spin-flip TDDFT.

$molecule 0 3 C 1.85082356 -1.78953123 0.00000000 H 2.38603593 -2.71605577 0.00000000 H 0.78082359 -1.78977646 0.00000000 C 2.52815456 -0.61573833 0.00000000 H 1.99294220 0.31078621 0.00000000 H 3.59815453 -0.61549310 0.00000000$end

$rem SPIN_FLIP true UNRESTRICTED true CIS_N_ROOTS 4 CIS_TRIPLETS false SET_ITER 50 CIS_DER_NUMSTATE 2 CALC_NAC true EXCHANGE bhhlyp BASIS 6-31G*$end

$derivative_coupling comment 1 3$end


Example 9.17  Nonadiabatic couplings between $S_{1}$ and $S_{2}$ states of ethylene computed via quadratic response theory at the TD-B3LYP level.

$molecule 0 1 C 1.85082356 -1.78953123 0.00000000 H 2.38603593 -2.71605577 0.00000000 H 0.78082359 -1.78977646 0.00000000 C 2.52815456 -0.61573833 0.00000000 H 1.99294220 0.31078621 0.00000000 H 3.59815453 -0.61549310 0.00000000$end

$rem CIS_N_ROOTS 4 CIS_TRIPLETS false RPA true SET_ITER 50 CIS_DER_NUMSTATE 2 CALC_NAC true EXCHANGE b3lyp BASIS 6-31G* SET_QUADRATIC true #include full quadratic response$end

$derivative_coupling comment 1 2$end