Projection-Based Embedding with Projected Atomic Orbitals

Abstract

The projected atomic orbitals (PAO) technique is presented for the construction of virtual orbital spaces in projection-based embedding applications. The proposed straightforward procedure produces a set of virtual orbitals, which is used in the final, high-level calculation of the embedded active subsystem. The PAO scheme is demonstrated on intermolecular potentials of bimolecular complexes, in ground and excited states, including Rydberg excitations. The results show the outstanding performance of the PbE embedding method with PAO virtual orbitals compared to those produced using common orbital localization techniques. The good agreement of the resulting PbE potential curves with those from high-level ab initio dimer calculations, also in diffuse basis sets, confirms that the PAO technique can be suggested for future applications of this type. The use of D3 dispersion corrections in such calculations is also proposed, supported by a superior accuracy over dispersion terms sourced from the effective fragment potential (EFP2) model.

Accuracy of projected atomic virtual orbital space in embedding applications

“…where P o is the projector of the entire occupied space of the supersystem (equivalent with RS), and P PAO 1 is the projector of the previously described subsystem virtual PAO space. This scheme has been implemented [27] in the MRCC program code [31,32].…”

“…In a recent work, [27] we suggested the use of projected atomic orbitals (PAOs) [28] as the strategy for producing the virtual orbital space of the active subsystem that should not suffer from this problem. In this paper we present this concept in detail and evaluate the different choices that impact the process of generating this orbital space.…”