Simple and Efficient Truncation of Virtual Spaces in Embedded Wave Functions via Concentric Localization

We present a strategy
to generate “concentrically local
orbitals” for the purpose of decreasing the computational cost
of wave function-in-density functional theory (WF-in-DFT) embedding.
The concentric localization is performed for the virtual orbitals
by first projecting the virtual space onto atomic orbitals centered
on the embedded atoms. Using a one-particle operator, these projected
orbitals are then taken as a starting point to iteratively span the
virtual space, recursively creating virtual orbital “shells”
with consecutively decreasing correlation energy recovery at each
iteration. This process can be repeated to convergence, allowing for
tunable accuracy. Assessment of the proposed scheme is performed by
application to the potential energy diagram of the Menshutkin reaction
of chloromethane and ammonia inside a segment of a carbon nanotube
and the torsional potential of a simplified version of the retinal
chromophore.