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5.11 Methods Based on “Constrained” DFT

5.11.4 Examples

(April 13, 2024)

Example 5.23  Charge separation on FAAQ

$molecule
   0 1
   C     -0.64570736     1.37641945    -0.59867467
   C      0.64047568     1.86965826    -0.50242683
   C      1.73542663     1.01169939    -0.26307089
   C      1.48977850    -0.39245666    -0.15200261
   C      0.17444585    -0.86520769    -0.27283957
   C     -0.91002699    -0.02021483    -0.46970395
   C      3.07770780     1.57576311    -0.14660056
   C      2.57383948    -1.35303134     0.09158744
   C      3.93006075    -0.78485926     0.20164558
   C      4.16915637     0.61104948     0.08827557
   C      5.48914671     1.09087541     0.20409492
   H      5.64130588     2.16192921     0.11315072
   C      6.54456054     0.22164774     0.42486947
   C      6.30689287    -1.16262761     0.53756193
   C      5.01647654    -1.65329553     0.42726664
   H     -1.45105590     2.07404495    -0.83914389
   H      0.85607395     2.92830339    -0.61585218
   H      0.02533661    -1.93964850    -0.19096085
   H      7.55839768     0.60647405     0.51134530
   H      7.13705743    -1.84392666     0.71043613
   H      4.80090178    -2.71421422     0.50926027
   O      2.35714021    -2.57891545     0.20103599
   O      3.29128460     2.80678842    -0.23826460
   C     -2.29106231    -0.63197545    -0.53957285
   O     -2.55084900    -1.72562847    -0.95628300
   N     -3.24209015     0.26680616     0.03199109
   H     -2.81592456     1.08883943     0.45966550
   C     -4.58411403     0.11982669     0.15424004
   C     -5.28753695     1.14948617     0.86238753
   C     -5.30144592    -0.99369577    -0.39253179
   C     -6.65078185     1.06387425     1.01814801
   H     -4.73058059     1.98862544     1.26980479
   C     -6.66791492    -1.05241167    -0.21955088
   H     -4.76132422    -1.76584307    -0.92242502
   C     -7.35245187    -0.03698606     0.47966072
   H     -7.18656323     1.84034269     1.55377875
   H     -7.22179827    -1.89092743    -0.62856041
   H     -8.42896369    -0.10082875     0.60432214
$end

$rem
   JOBTYPE         FORCE
   METHOD          B3LYP
   BASIS           6-31G*
   SCF_PRINT       TRUE
   CDFT            TRUE
$end

$cdft
   2
   1   1  25
  -1  26  38
$end

The value of 2 under $cdft section in the FAAQ example represents the constraint. The valules, 1 and -1, represent the coefficients for fragment charges. Suppose the first fragment consists of atom 1–25 with A excess electrons, and the second fragment consists of atom 26–38 with B excess electrons. The $cdft section can be viewd as a system of linear equations as follows:

(𝟏)*A+(-𝟏)*B =𝟐
A+B =0

The second equation is zero because the FAAQ is neutral. by solving the system of linear equations, one gets A = 1, and B = -1. However, the $cdft section is equivalent to the following one.

$cdft
1
1 1  25
-1
1 26 38
$end

Example 5.24  Cu2-Ox High Spin

$molecule
   2 3
   Cu      1.4674     1.6370     1.5762
   O       1.7093     0.0850     0.3825
   O      -0.5891     1.3402     0.9352
   C       0.6487    -0.3651    -0.1716
   N       1.2005     3.2680     2.7240
   N       3.0386     2.6879     0.6981
   N       1.3597     0.4651     3.4308
   H       2.1491    -0.1464     3.4851
   H       0.5184    -0.0755     3.4352
   H       1.3626     1.0836     4.2166
   H       1.9316     3.3202     3.4043
   H       0.3168     3.2079     3.1883
   H       1.2204     4.0865     2.1499
   H       3.8375     2.6565     1.2987
   H       3.2668     2.2722    -0.1823
   H       2.7652     3.6394     0.5565
   Cu     -1.4674    -1.6370    -1.5762
   O      -1.7093    -0.0850    -0.3825
   O       0.5891    -1.3402    -0.9352
   C      -0.6487     0.3651     0.1716
   N      -1.2005    -3.2680    -2.7240
   N      -3.0386    -2.6879    -0.6981
   N      -1.3597    -0.4651    -3.4308
   H      -2.6704    -3.4097    -0.1120
   H      -3.6070    -3.0961    -1.4124
   H      -3.5921    -2.0622    -0.1485
   H      -0.3622    -3.1653    -3.2595
   H      -1.9799    -3.3721    -3.3417
   H      -1.1266    -4.0773    -2.1412
   H      -0.5359     0.1017    -3.4196
   H      -2.1667     0.1211    -3.5020
   H      -1.3275    -1.0845    -4.2152
$end

$rem
   METHOD          B3LYP
   BASIS           6-31G*
   SCF_PRINT       TRUE
   CDFT            TRUE
$end

$cdft
   2
   1   1   3  s
  -1  17  19  s
$end

Example 5.25  Constrained DFT with FBH charges applied to F-H2O interaction

$molecule
   -1 1
--
   -1 1
   F         1.2344377204   -0.0287603388    0.0000000000
--
   0 1
   O        -1.2152661043    0.1159898799    0.0000000000
   H        -0.1545755250    0.1042552996    0.0000000000
   H        -1.3911772011   -0.8334364448    0.0000000000
$end

$rem
   METHOD       hf
   BASIS        aug-cc-pvtz
   XC_GRID      3
   CDFT         true
   CDFT_POP     fbh
   NO_REORIENT  true
point_group_symmetry False
integral_symmetry false
$end

$cdft
   1.0
   1 1 1
   0.0
   1 1 1 s
$end