A Multimer Embedding Approach for Energies, Structures, and Vibrational Properties of Molecular Crystals

Accurate calculations of molecular crystals are crucial for crystal engineering and drug design. However, high-level electronic structure calculations are often prohibitively expensive for relevant systems. Such expensive periodic calculations can be circumvented by the usage of embedding methods. For instance, the periodic result of a high-level method can be approximated by a subtractive embedding scheme, in which a fully periodic calculation is only performed using a less expensive lower-level method and then monomer energies and dimer interaction energies are replaced by those of the high-level method. Herein, we present such a multimer embedding approach containing up to trimer interactions for energies, structures, and vibrational properties of molecular crystals. We demonstrate the high accuracy of this approach for the X23 benchmark set of molecular crystals by approximating a periodic hybrid density functional (PBE0+MBD) by embedding multimers into less expensive calculations using a generalized-gradient approximation (GGA) functional (PBE+MBD). We show that trimer interactions are crucial for accurate lattice energies and cell volumes, while harmonic vibrational properties can already be well captured at the dimer level. Finally, we use this multimer embedding approach to also incorporate anharmonic effects.