The “XSAPT” method, which may be regarded either as an acronym for
“XPol+SAPT” or for “extended” symmetry adapted perturbation theory (SAPT),
was originally introduced by Jacobson and Herbert
557
J. Chem. Phys.
(2011),
134,
pp. 094118.
Link
,
498
Phys. Chem. Chem. Phys.
(2012),
14,
pp. 7679.
Link
as a low-scaling, systematically-improvable method for intermolecular interactions that
could be applicable to large systems. The idea was
to replace the need for empirical parameters in the XPol method with
on-the-fly evaluation of exchange-repulsion and dispersion interactions via
pairwise-additive SAPT. Stated differently, XSAPT uses XPol to evaluate many-body
(non-pairwise-additive) polarization effects, but then assumes that dispersion
and exchange-repulsion interactions are pairwise additive, and
evaluates them via pairwise SAPT0 or SAPT0(KS) calculations.
The method was significantly extended by Lao, Herbert, and
co-workers,
688
J. Phys. Chem. Lett.
(2012),
3,
pp. 3241.
Link
,
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(2013),
139,
pp. 034107.
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,
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J. Phys. Chem. A
(2015),
119,
pp. 235.
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,
693
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(2018),
14,
pp. 2955.
Link
,
694
J. Chem. Theory Comput.
(2018),
14,
pp. 5128.
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,
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(2019),
10,
pp. 2706.
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,
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151,
pp. 031102.
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,
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(2021),
155,
pp. 034103.
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with various approximations applied in place of the SAPT0 or SAPT0(KS) dispersion terms,
173
Acc. Chem. Res.
(2021),
54,
pp. 3679.
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which are both the least accurate and most expensive contributions to second-order SAPT.
Overviews of of XSAPT-based methods can be found in Refs.
691
J. Phys. Chem. A
(2015),
119,
pp. 235.
Link
and
173
Acc. Chem. Res.
(2021),
54,
pp. 3679.
Link
and implementation details can be found in
Refs.
498
Phys. Chem. Chem. Phys.
(2012),
14,
pp. 7679.
Link
,
693
J. Chem. Theory Comput.
(2018),
14,
pp. 2955.
Link
, and
765
J. Chem. Phys.
(2019),
151,
pp. 031102.
Link
.
In particular, the XSAPT+MBD method
174
J. Phys. Chem. Lett.
(2019),
10,
pp. 2706.
Link
stands out as a way to obtain qualitative insight
about noncovalent interactions in large systems, backed by quantitative energetics calculations.
173
Acc. Chem. Res.
(2021),
54,
pp. 3679.
Link
In many cases, this type of analysis has upended textbook “conventional wisdom", as reviewed in Ref.
506
J. Phys. Chem. A
(2021),
125,
pp. 7125.
Link
.