Efficient EOM-CC-based Protocol for the Calculation of Electron Affinity of Solvated Nucleobases: Uracil as a Case Study

We present an explicit solvation
protocol for the calculation of
electron affinity values of the solvated nucleobases. The protocol
uses a quantum mechanics/molecular mechanics (QM/MM) approach based
on the newly implemented domain-based pair natural orbital EOM-CCSD
(equation-of-motion coupled-cluster single–double) method.
The stability of the solvated nucleobase anion is sensitive to the
local distribution of the water molecules around the nucleobase, and
the calculated electron affinity values converge slowly with respect
to the number of snapshots and the size of the water box. The use
of nonpolarizable water molecules leads to an overestimation of the
electron affinity and makes the result sensitive to the size of the
QM region in the QM/MM calculation. The electron affinity values,
although sensitive to the size of the basis set, lead to an almost
constant blue shift of the electron affinity upon the increase in
the basis set. The present protocol allows for a controllable description
of the various parameters affecting the electron affinity value, and
the calculated adiabatic electron affinity values are in excellent
agreement with experimental results.