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# 12.17.3 Examples

(February 4, 2022)

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 12.12 and illustrated in the following example.

Example 12.42  Example showing singlet excited state calculation, on (H${}_{2}$O)${}_{4}$. 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


View output

The multi-exciton keyword AIFDEM_SINGFIS invokes the use of multi-exciton states, $|^{1}(\Phi_{\!A}^{\text{T}}\Phi_{\!B}^{\text{T}})\Phi_{\!C}\ldots\rangle$. The following example illustrates this, along with the use of AIFDEM_SEGSTART and AIFDEM_SEGEND to split up the calculation of matrix elements into segments. This is required for multi-exciton calculations.

Example 12.43  AIFDEM example with multi-exciton states in the basis.

$rem BASIS aug-cc-pvdz EXCHANGE HF CIS_N_ROOTS 3 CIS_SINGLETS TRUE CIS_TRIPLETS TRUE XPOL TRUE AIFDEM TRUE AIFDEM_EMBED_RANGE 0 AIFDEM_NTOTHRESH 90 NTO_PAIRS 1 AIFDEM_SINGFIS TRUE AIFDEM_CTSTATES TRUE SCF_PRINT_FRGM true AIFDEM_SEGSTART 1 AIFDEM_SEGEND 2$end

$molecule 0 1 -- H2O 0 0 1 O 1.74078 1.59716 -1.49814 H 2.22908 2.18316 -2.08914 H 0.88038 2.04726 -1.32684 -- H2O 1 0 1 O 1.31998 -1.18934 -1.91734 H 1.49988 -0.22974 -1.89044 H 1.69058 -1.52594 -1.07704$end

$xpol embed charges charges chelpg$end


View output

To compute AIFDEM derivatives $\mathbf{H}^{[x]}$ and $\mathbf{S}^{[x]}$ 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; therefore, 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 12.44 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


View output