Dissociation Energies\nvia Embedding Techniques

Due to the large number of interactions, evaluating interaction\nenergies for large or periodic systems results in time-consuming calculations.\nPrime examples are liquids, adsorbates, and molecular crystals. Thus,\nthere is a high demand for a cheap but still accurate method to determine\ninteraction energies and gradients. One approach to counteract the\ncomputational cost is to fragment a large cluster into smaller subsystems,\nsometimes called many-body expansion, with the fragments being molecules\nor parts thereof. These subsystems can then be embedded into larger\nentities, representing the bigger system. In this work, we test several\nsubsystem approaches and explore their limits and behaviors, determined\nby calculations of trimer interaction energies. The methods presented\nhere encompass mechanical embedding, point charges, polarizable embedding,\npolarizable density embedding, and density embedding. We evaluate\nnonembedded fragmentation, QM/MM (quantum mechanics/molecular mechanics),\nand QM/QM (quantum mechanics/quantum mechanics) embedding theories.\nFinally, we make use of symmetry-adapted perturbation theory utilizing\ndensity functional theory for the monomers to interpret the results.\nDepending on the strength of the interaction, different embedding\nmethods and schemes prove favorable to accurately describe a system.\nThe embedding approaches presented here are able to decrease the interaction\nenergy errors with respect to full system calculations by a factor\nof up to 20 in comparison to simple/unembedded approaches, leading\nto errors below 0.1 kJ/mol.