Molecular tailoring approach in conjunction with MP2 and Ri-MP2 codes: a comparison with fragment molecular orbital method

Abstract

Many Divide-and-Conquer based approaches are being developed to overcome the high scaling problem of the ab initio methods. In this work, one such method, Molecular Tailoring Approach (MTA) has been interfaced with recently developed efficient Moller-Plesset second order perturbation theory (MP2) codes viz. IMS-MP2 and RI-MP2 to reap the advantage of both. An external driver script is developed for implementing MTA at the front-end and the MP2 codes at the back-end. The present version of the driver script is written only for a single point energy evaluation of a molecular system at a fixed geometry. The performance of these newly developed MTA-IMS-MP2 and MTA-RI-MP2 codes is extensively benchmarked for a variety of molecular systems vis-a-vis the corresponding actual runs. In addition to this, the performance of these programs is also critically compared with Fragment Molecular Orbital (FMO), another popular fragment-based method. It is observed that FMO2/2 is superior to FMO3/2 and MTA with respect to time advantage; however, the errors of FMO2 are much beyond chemical accuracy. However, FMO3/2 is a highly accurate method for biological systems but is unsuccessful in case of water clusters. MTA produces estimates with errors within 1 kcal/mol uniformly for all systems with reasonable time advantage. Analysis carried out employing various basis sets shows that FMO gives its optimum performance only for basis sets, which does not include diffuse functions. On the contrary, MTA performance is found to be similar for any basis set used.