Analyze Intermolecular Interactions by SAPT
This is a quick note of how to analyze intermolecular interaction by Sysmetry-Adapted Perturbation Theory (SAPT) using Psi4.
1. Preface
SAPT can divide intermolecular interaction into 4 components:
- Electrostatics: describes the classical Coulomb interaction between fragments, with positive or negative values.
- Exchange: describes the short-range exchange repulsion between fragments, with positive values (i.e. unfavorable for binding).
- Dispersion: has a negative value and acts as an attractive force.
- Induction: reflects the polarization and transfer of charges between fragments, with a negative value.
The SAPT theory involves intramolecular and intermolecular perturbations, and as the order of perturbations increases, the results get better. In principle (as the order of perturbations considered increases step by step), the accuracy order is SAPT0, SAPT2, SAPT2+, SAPT2+(3), SAPT2+3. SAPT0 can still be used for medium to moderately large systems, while SAPT2+(3) can only be used for small systems.
In order to improve the accuracy of SAPT interaction calculations, the SAPT0 in the Psi4 program also includes the δHF term, which reflects the high-order induction effect. For high-order SAPT such as SAPT2+, SAPT2+(3), SAPT2+3, the δMP2 term can also be added to consider the high-order coupling between induction and dispersion, such as SAPT2+(3) combined with δMP2 called SAPT2+(3)δMP2. However, the physical meaning of the δ term is not very clear and cannot be further divided. The numerical value of the δ term is usually small, and it is generally classified as an induction term.
2. Input
An example is shown following:
memory 20 gb
molecule dimer {
0 1
S 1.318033 5.842267 2.881214
N -1.355505 5.579081 0.154536
H -1.976421 5.935383 -0.153845
C -0.705457 6.014672 1.291775
C -0.905384 7.050266 2.235758
H -1.629222 7.634376 2.237331
C -0.563794 4.592784 -0.398267
C 0.472970 5.283299 1.488835
C 0.120527 7.070918 3.149491
H 0.169447 7.685226 3.846026
S -1.318033 3.137133 -2.881214
N 1.355505 3.400319 -0.154536
H 1.976421 3.044017 0.153845
C 0.705457 2.964728 -1.291775
C 0.905384 1.929134 -2.235758
H 1.629222 1.345024 -2.237331
C 0.563794 4.386616 0.398267
C -0.472970 3.696101 -1.488835
C -0.120527 1.908482 -3.149491
H -0.169447 1.294174 -3.846026
--
0 1
S 4.174133 -1.352567 -2.881214
N 1.500595 -1.089381 -0.154536
H 0.879679 -1.445683 0.153845
C 2.150643 -1.524972 -1.291775
C 1.950716 -2.560566 -2.235758
H 1.226878 -3.144676 -2.237331
C 2.292306 -0.103084 0.398267
C 3.329070 -0.793599 -1.488835
C 2.976627 -2.581218 -3.149491
H 3.025547 -3.195526 -3.846026
S 1.538067 1.352567 2.881214
N 4.211605 1.089381 0.154536
H 4.832521 1.445683 -0.153845
C 3.561557 1.524972 1.291775
C 3.761484 2.560566 2.235758
H 4.485322 3.144676 2.237331
C 3.419894 0.103084 -0.398267
C 2.383130 0.793599 1.488835
C 2.735573 2.581218 3.149491
H 2.686653 3.195526 3.846026
units angstrom
}
set {
basis jun-cc-pVDZ
scf_type DF
freeze_core True
}
energy('sapt0')
-
freeze_core Truecan save computational cost. -
scf_type DFcan utilize density fitting to accelerate the SCF process.
Run command psi4 xxx.inp xxx.out -n 8 to start the calculation using 8 cores.
3. Output
The SAPT results would be summarized as following.
Special recipe for scaled SAPT0 (see Manual):
Electrostatics sSAPT0 -24.34792103 [mEh] -15.27855111 [kcal/mol] -63.92545785 [kJ/mol]
Exchange sSAPT0 15.70145759 [mEh] 9.85281339 [kcal/mol] 41.22417122 [kJ/mol]
Induction sSAPT0 -5.93603581 [mEh] -3.72491871 [kcal/mol] -15.58505986 [kJ/mol]
Dispersion sSAPT0 -4.77805738 [mEh] -2.99827627 [kcal/mol] -12.54478793 [kJ/mol]
Total sSAPT0 -19.36055663 [mEh] -12.14893270 [kcal/mol] -50.83113444 [kJ/mol]
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