13.10 ALMO-EDA Involving Excited-State Molecules

13.10.2 Job Control

The ALMO-EDA for intermolecular interactions involving excited-state molecules implemented in Q-Chem 5.1 supports CIS and TDDFT within the Tamm-Dancoff approximation (TDA) for closed-shell systems, i.e., excited states calculated by TDDFT and unrestricted systems are currently not supported. The EDA procedure is triggered by setting EX_EDA to TRUE. The code first performs a customized ground-state calculation (using AO-based ALMOs) through the “EDA2" driver. During the isolated fragment calculations in this EDA, the fragment excited states are also computed after its ground-state SCF is converged, which is controlled by a new input section $frgm_cis_n_roots. The format of this input section is as follows:

$frgm_cis_n_roots
¯frgm_idx1¯¯nstates_to_calc¯¯nstates_as_exciton_basis
¯frgm_idx2¯¯nstates_to_calc¯¯nstates_as_exciton_basis
¯.  .  .
$end

Here “nstates_to_calc" specifies the number of states to calculate for each fragment (the value of CIS_N_ROOTS for each fragment calculation), and “nstates_as_exciton_basis" refers to the number of calculated fragment states that are used to construct the EXSP state (whose sum gives M in eqn. 13.26). When the supersystem is considered as an exciplex where the excitation is assigned to a specific fragment, only one row is needed in this section, and there is no need to specify the number of states used as the basis for the EXSP state.

The other relevant rem variables includes CIS_N_ROOTS, which specifies the number of roots to calculate in the ALMO-CIS/TDA and full CIS/TDA calculations, and EIGSLV_METH (see Sec. 13.18) that is set to 1 (using the Davidson iterative solver) by default. Note that the number of states that the EDA is concerned with is controlled by the number of isolated fragment states (the exciplex case) or the total number of states that are excitonically coupled (the excimer case). In the latter case, CIS_N_ROOTS is usually set to a value that is larger than M to ensure that all states of interest are captured in the ALMO-CIS/TDA and full CIS/TDA calculations, as changes in state-ordering might occur.

EX_EDA
       Perform an ALMO-EDA calculation with one or more fragments excited.
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE Perform EDA with excited-state molecule(s) taken into account. FALSE
RECOMMENDATION:
       None

Example 13.22  EDA for the lowest two excited states of the formamide-water complex at the CIS/6-31+G(d) level of theory. Both excited states are assigned to the formamide molecule and the system is regarded as an exciplex.

$molecule
0 1
--
0 1
C         1.1508059365    0.2982718924    0.0240277739
O         0.3545181649    1.2334803420   -0.0015882208
N         0.8104369587   -1.0072797234    0.0043506838
H         2.2327270535    0.4686363261    0.0666232655
H        -0.1675092286   -1.2596328526   -0.0352400180
H         1.5210524537   -1.7122494331    0.0139809901
--
0 1
O        -1.9693273428   -0.2999882700   -0.2293071572
H        -1.3827632725    0.4697313642   -0.1375254289
H        -2.7470364523   -0.0962178118    0.2907490329
$end

$rem
jobtype eda
ex_eda  true
method   hf
basis       6-31+g(d)
sym_ignore  true
symmetry    false
scf_convergence 8
cis_n_roots     2
cis_triplets   false
thresh         12
$end

$frgm_cis_n_roots
1  2
$end

Example 13.23  EDA for the lowest two states (1s->2s) of the He2 excimer computed at the CIS/6-311(2+,2+)G (customized) level of theory. For each He, eight excited states are calculated and only the lowest one is used to construct the EXSP state, giving rise to two supersystem states.

$molecule
0 1
--
0 1
He    0.0   0.0  0.0
--
0 1
He    3.0   0.0  0.0
$end

$rem
   JOBTYPE        eda
   EX_EDA         true
   METHOD         hf
   BASIS          gen   !6-311(2+,2+)G
   SYM_IGNORE     true
   SYMMETRY       false
   CIS_N_ROOTS    8
   CIS_TRIPLETS   false
   THRESH         12
   EIGSLV_METH    0   !direct
$end

$frgm_cis_n_roots
1  8  1
2  8  1
$end

$basis
He   0
S    3    1.000000
9.81243000E+01    2.87452000E-02
1.47689000E+01    2.08061000E-01
3.31883000E+00    8.37635000E-01
S    1    1.000000
8.74047000E-01    1.00000000E+00
S    1    1.000000
2.44564000E-01    1.00000000E+00
SP   1    1.000000
4.80000000E-02    1.00000000E+00   1.00000000E+00
SP   1    1.000000
1.44578313E-02    1.00000000E+00   1.00000000E+00
****
$end