In donor–acceptor (D–A) materials, the overlap between the donor orbital
(HOMO of D) and the acceptor orbital (LUMO of A) has been shown to correlate
with excited-state charge-transfer character.
1249
J. Phys. Chem. Lett.
(2023),
14,
pp. 11063–11068.
Link
This overlap can be
computed, taking into account relaxation of the monomer geometries upon formation
of the D–A complex, using the $rem variable
MO_OVERLAPS_TWO_GEOMS, as shown in
Example 10.3.3 below. This requires two separate SCF calculations (one for
either D or A in isolation, and another for the dimer D–A), and both calculations must use
the same basis set. Therefore, ghost atoms should be added in the monomer calculation
so that both SCF calculations use the dimer basis set. Output is delivered in a directory
OutputName.MO-overlaps (where OutputName is the name of the Q-Chem
output file). This output consists of the -spin MO coefficients for both systems
(CA-Geom1.txt and CA-Geom2.txt), the AO overlap matrix between the
two calculations (AO-overlap-TwoGeoms.txt, which need not be an identity matrix
because the geometries could differ), and the MO overlap matrix between the two calculations
(MO-overlap-TwoGeoms.txt).
Note: Currently, only overlaps between -spin MOs are considered, hence why only -spin MO coefficients are returned. This means that this features is implemented only for spin-restricted wave functions.
Alternatively, one might be interested in the degree of spatial overlap between donor and acceptor orbitals (e.g., HOMO and LUMO) within the same molecule or on two different molecules within the same supramolecular calculation. These can be computed using the same tools that are used to compute the metric in TDDFT [Eq. (7.16)], and the contributing overlaps [Eq. (7.17)] can be printed using SPATIAL_OVERLAP_ANALYSIS. See Section 7.3.4.1 for job control options and Example 10.3.3 for an example.
MO_OVERLAPS_TWO_GEOMS
MO_OVERLAPS_TWO_GEOMS
Specifies whether to compute molecular orbital overlaps at two different geometries.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0
Do not compute these overlaps.
1
Used to indicate the first of two required SCF calculations.
2
Used to indicate the second of two required SCF calculations.
RECOMMENDATION:
The atoms must be ordered in the same way for both calculations. (This is not checked.)
Example 10.10 Compute “spatial overlaps” of the frontier MOs, for a dimer of naphthalene and tetracyanoquinone. These are overlaps of the absolute values of the orbitals [ Eq. (7.17)]. This feature is based on the metric of TDDFT, therefore at least one excited state must be computed in order to trigger this analysis.
$molecule 0 1 C 1.262951 1.945976 -0.561360 C 0.648393 2.896730 0.296837 C 2.662678 1.710349 -0.545738 H 3.283172 2.277769 0.142405 C 3.225026 0.771942 -1.373626 H 4.295659 0.593998 -1.345666 C 2.415782 0.024414 -2.263235 H 2.874995 -0.720497 -2.905219 C 1.061881 0.234151 -2.304223 H 0.435114 -0.339033 -2.982450 C 0.449076 1.198213 -1.458953 C -0.950361 1.427044 -1.468096 C -1.241593 -0.113527 1.511623 H -1.776720 0.630886 2.090246 C 0.087508 -0.255323 1.653805 H 0.634524 0.372807 2.348013 C 0.826509 -1.220978 0.861471 C 2.186874 -1.336026 0.974224 C 0.076113 -2.057065 -0.061488 H 0.616720 -2.788316 -0.652909 C -1.255888 -1.926290 -0.191214 H -1.804801 -2.556542 -0.883200 C -1.987167 -0.926165 0.566999 C -3.333669 -0.739067 0.378968 C -1.516839 2.349538 -0.623777 C -0.708145 3.093806 0.267607 H 1.274799 3.469589 0.975647 H -1.571143 0.856542 -2.154642 H -2.590617 2.512925 -0.634219 H -1.169539 3.821896 0.927541 C 2.935702 -0.523467 1.883035 C 2.933880 -2.256250 0.173594 N 3.523004 0.145261 2.626355 N 3.522832 -3.002457 -0.490547 C -4.043584 0.294041 1.066080 C -4.077033 -1.521605 -0.558360 N -4.657467 -2.163965 -1.330296 N -4.588038 1.154569 1.621873 $end $rem method wb97x-d basis 6-31G* cis_triplets false cis_n_roots 1 ! needed for spatial overlap analysis spatial_overlap_anal true spatial_overlap_print 1 $end
Example 10.11 Compute MO overlaps for a CHCF dimer.
$comment
Job 1: this is the dimer
$end
$molecule
0 1
C -0.6656405432 -0.0000000000 -3.3601967383
H -1.2362909837 -0.9253767714 -3.3623091560
H -1.2362909837 0.9253767714 -3.3623091560
C 0.6656405432 0.0000000000 -3.3601967383
H 1.2362909837 0.9253767714 -3.3623091560
H 1.2362909837 -0.9253767714 -3.3623091560
C -0.6610251661 -0.0000000000 1.1109504097
F -1.3861639022 -1.1014627457 1.1119323203
F -1.3861639022 1.1014627457 1.1119323203
C 0.6610251661 -0.0000000000 1.1109504097
F 1.3861639022 1.1014627457 1.1119323203
F 1.3861639022 -1.1014627457 1.1119323203
$end
$rem
method¯¯cam-b3lyp
basis¯¯6-31+G*
mo_overlaps_two_geoms 1 ! for job #1
$end
@@@
$comment
Job 2: monomer1, with ghost functions for monomer2
$end
$molecule
0 1
C -0.6656405432 -0.0000000000 -3.3601967383
H -1.2362909837 -0.9253767714 -3.3623091560
H -1.2362909837 0.9253767714 -3.3623091560
C 0.6656405432 0.0000000000 -3.3601967383
H 1.2362909837 0.9253767714 -3.3623091560
H 1.2362909837 -0.9253767714 -3.3623091560
@C -0.6610251661 -0.0000000000 1.1109504097
@F -1.3861639022 -1.1014627457 1.1119323203
@F -1.3861639022 1.1014627457 1.1119323203
@C 0.6610251661 -0.0000000000 1.1109504097
@F 1.3861639022 1.1014627457 1.1119323203
@F 1.3861639022 -1.1014627457 1.1119323203
$end
$rem
method cam-b3lyp
basis 6-31+G*
mo_overlaps_two_geoms 2 ! for job #2
$end