A basic AIFDEM calculation is requested by setting AIFDEM = TRUE in the $rem section, with additional job-control variables as described below.
A basic AIFDEM calculation is requested by setting AIFDEM = TRUE in the $rem section, with additional job-control variables as described below.
AIFDEM
Perform an AIFDEM calculation.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE
Do not perform an AIFDEM calculation.
TRUE
Perform an AIFDEM calculation.
RECOMMENDATION:
False
AIFDEM_NTOTHRESH
Controls the number of NTOs that are retained in the
exciton-site basis states.
TYPE:
INTEGER
DEFAULT:
99
OPTIONS:
Threshold percentage of the norm of fragment NTO amplitudes.
RECOMMENDATION:
A threshold of gives a good trade-off of computational time and
accuracy for organic molecules.
AIFDEM_EMBED_RANGE
Specifies the size of the QM region for charge embedding
TYPE:
INTEGER
DEFAULT:
FULL_QM
OPTIONS:
FULL_QM
No charge embedding.
0
Treat only excited fragments with QM.
Range (in Å) from excited fragments within which to
treat other fragments with QM.
RECOMMENDATION:
The minimal threshold of zero Å typically
maintains accuracy while significantly reducing computational time.
AIFDEM_CTSTATES
Include charge-transfer-like cation/anion pair states
in the AIFDEM basis.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
TRUE
Include CT states.
FALSE
Do not include CT states.
RECOMMENDATION:
None
For charge-embedded AIFDEM calculations, set XPOL = TRUE in the $rem section and then select the type of embedding charges via the $xpol input section, as described in Section 13.11 and illustrated in the following example.
Example 13.34 Example showing singlet excited state calculation, on (HO). XPol is used to generate monomer wave functions with ChElPG charges. Minimal QM charge embedding is used for the exciton model with three excited states per fragment.
$molecule 0 1 --H2O 0 0 1 O 1.74078 1.59716 -1.49814 H 2.22908 2.18316 -2.08914 H 0.88038 2.04726 -1.32684 --H2O 1 0 1 O 1.31998 -1.18934 -1.91734 H 1.49988 -0.22974 -1.89044 H 1.69058 -1.52594 -1.07704 --H2O 2 0 1 O -0.68982 2.59476 -0.72224 H -1.14372 3.37086 -1.07364 H -1.35592 1.84986 -0.78334 --H2O 3 0 1 O -1.27512 -1.77394 -1.69524 H -0.32252 -1.52884 -1.85604 H -1.53992 -2.30454 -2.45644 $end $rem BASIS aug-cc-pvdz EXCHANGE HF CIS_N_ROOTS 3 CIS_TRIPLETS FALSE XPOL TRUE AIFDEM TRUE AIFDEM_EMBED_RANGE 0 AIFDEM_NTOTHRESH 90 NTO_PAIRS 1 $end $xpol embed charges charges CHELPG $end
To compute AIFDEM derivatives and of the Hamiltonian and overlap matrices, the user should request a standard AIFDEM job and in addition set CIS_STATE_DERIV = 1. Currently, the AIFDEM derivatives do not support charge embedding so the keyword AIFDEM_EMBED_RANGE must be omitted from these jobs, which precludes the use of XPol wavefunctions for the fragments. Furthermore, only one excited state per fragment is supported so the keyword CIS_N_ROOTS = 1. is required.
The derivatives of the AIFDEM Hamiltonian matrix and overlap matrix are printed in the output file in sets of the three Cartesian coordinates that belong to a single atom. For convenience, the orthogonalized AIFDEM Hamiltonian matrix elements are saved in the scratch directory, $QCSCRATCH/aifdem_deriv. These are organized such that the derivatives for each unique matrix element are stored in individual files in the order of the atomic Cartesian coordinates. These files can facilitate external calculation of exciton/phonon coupling constants.
Example 13.35 A basic AIFDEM derivative calculation on a chain of helium atoms.
$molecule 0 1 --frgm 0 0 1 He 0.000 0.000 0.000 He 0.000 0.000 1.400 --frgm 1 0 1 He 0.000 0.000 2.800 He 0.000 0.000 4.200 $end $rem BASIS = cc-pvdz EXCHANGE = hf AIFDEM = true CIS_N_ROOTS = 1 CIS_SINGLETS = true CIS_TRIPLETS = false CIS_STATE_DERIV = 1 NTO_PAIRS = 1 MEM_TOTAL = 1000 MEM_STATIC = 1000 MAX_CIS_CYCLES = 200 MAX_SCF_CYCLES = 200 THRESH = 10 AIFDEM_NTOTHRESH = 100 $end