A computational study of hexachlorobenzene-soil organic matter-interactions

The fate of hexachlorobenzene (HCB) in soil represents a critical environmental problem. Once HCB has reached the soil it will interact with soil constituents, especially soil organic matter (SOM). The understanding of this interaction is important for choosing effective remediation procedures. Here we report a study of binding of HCB to a test set of molecules, which was developed to mimic representative functional groups of SOM. The binding energy of complexes formed by HCB and the test set molecules were investigated at different levels of theory. Effects of different types of dispersion correction to DFT, basis sets and DFT-functionals have been studied. Moreover, the general ability of dispersion-corrected DFT to represent this interaction has been benchmarked against methods such as MP2 and CCSD. As a result the B3LYP-D3 dispersion correction combined with the 6-311++G(2d,2p) basis set was found to be a compromise between accuracy and efficiency and it is recommended for studying this type of non-covalent interaction. Moreover, the performance of the GROMOS force field in the description of this interaction has been tested.