Intersystem crossing opt

TD-DFT

#----------------------------------------------------------------------
# Gradient projection method for ISC between S0 and T1 by TDDFT BHHLYP/6-31G
#

$COMPASS 
Title
 C2H4 Molecule test run
Basis
 6-31G
Geometry
C            -0.00000141      0.00000353      0.72393424
C             0.00000417     -0.00000109     -0.72393515
H             0.73780975     -0.54421247      1.29907106
H            -0.73778145      0.54421417      1.29907329
H             0.73777374      0.54421576     -1.29907129
H            -0.73779427     -0.54423609     -1.29906321
END geometry
nosym
skeleton
$END

$bdfopt
iprt
 3
imulti
2    # set 1: Penalty function method
maxcycle
50
tolgrad
1.d-4
tolstep
5.d-3
tolene
1.d-6
noncouple  # need not interstate coupling gradient which is default for imulti = 1
$end

$xuanyuan
direct
$end

$SCF
RKS
charge
 0
spin
 1
atomorb
DFT
BHHLYP
$END

$resp
geom
norder
 1
method
 1
$end

$tddft
imethod
 1
isf
 1
nexit 
 5
itda
 1
idiag
 1
istore
 1
crit_e
 1.d-8
crit_vec
 1.d-6
lefteig
ialda
4
$end

$resp
geom
norder
 1
method
 2
iroot
 1 
$end

Alternatively, the T1 state can be described by SCF:

#----------------------------------------------------------------------
# Gradient projection method for ISC between S0 and T1 by BHHLYP/6-31G
#

$COMPASS 
Title
 C2H4 Molecule test run
Basis
 6-31G
Geometry
C            -0.00000141      0.00000353      0.72393424
C             0.00000417     -0.00000109     -0.72393515
H             0.73780975     -0.54421247      1.29907106
H            -0.73778145      0.54421417      1.29907329
H             0.73777374      0.54421576     -1.29907129
H            -0.73779427     -0.54423609     -1.29906321
END geometry
nosym
skeleton
$END

$bdfopt
iprt
 3
imulti
2
maxcycle
50
tolgrad
1.d-4
tolstep
5.d-3
tolene
1.d-6
noncouple
$end

$xuanyuan
direct
$end

$SCF
RKS
charge
 0
spin
 1
atomorb
DFT
BHHLYP
$END

$resp
geom
norder
 1
method
 1
$end

$SCF
UKS
charge
 0
spin
 3
atomorb
DFT
BHHLYP
$END

$resp
geom
norder
 1
method
 1
$end

CASSCF

#----------------------------------------------------------------------
# Gradient projection method for ISC between S0 and T1 by SA2-CASSCF(4,4)/6-31G
#

$COMPASS
Title
 C6H6 test run, cc-pvdz
Basis
6-31G
Geometry
C             0.00000373      0.00000493      0.66789017
C            -0.00001203     -0.00000431     -0.66791647
H             0.71651373     -0.53471753      1.31749034
H            -0.71649838      0.53472410      1.31749465
H             0.71707430      0.53383897     -1.31766051
H            -0.71710642     -0.53387717     -1.31763176
End geometry
nosym
norotate
saorb
$END

$bdfopt
iprt
 3
imulti
 2
tolgrad
1.d-4
tolstep
5.d-3
tolene
1.d-5
noncouple
$end

$XUANYUAN
$END

$SCF
rhf
spin
1
atomorb
$END

$MCSCF
close
 6 
active
 4
actele
 4
mixci
 2  
 1 3
 1 1
 1 1 
ROOTPRT
 1
roots
2 2 1
prtcri
0.1
molden
guess
read
$END

$grad
nrootgrad
1  
double
maxiter
500
mxiter
200
cutcpmc
1.d-4
$end

$grad
nrootgrad
2
double  
maxiter
500
mxiter
200
cutcpmc
1.d-4
$end