Projection-Based Embedding with Projected Atomic Orbitals

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.