Cluster-in-Molecule Local Correlation Method with an Accurate Distant Pair Correction for Large Systems

The cluster-in-molecule (CIM) local
correlation approach with an
accurate distant pair correlation energy correction is presented.
For large systems, the inclusion of distant pair correlation energies
is essential for the accurate prediction of absolute correlation energies
and relative energies. Here, we propose a simple and efficient scheme
for evaluating the distant pair correlation energy correction for
the CIM approaches. The corrections can be readily extracted from
electron correlation calculations of clusters with almost no additional
effort. Benchmark calculations show that the improved CIM approach
can recover more than 99.94% of the correlation energy calculated
by the parent method. By combining the CIM approach with the domain-based
local pair natural orbital (DLPNO) local correlation approach, we
have provided accurate binding energies at the CIM-DLPNO-CCSD­(T) level
for a test set consisting of eight weakly bound complexes ranging
in size from 200 to 1027 atoms. With these results as the reference
data, the accuracy and applicability of other electron correlation
methods and a few density functional methods for large systems have
been assessed.