In comparison, the MT potential performs better and is consistent between HF and MP2c contributions, most presumably thanks to the explicit cancellation of the G = 0 singularity and the directional effects of the screening function Φ long (G) -Φ long (G). Expanding an orthorhombic box around the electron density coupled to the MT Poisson solver allows to converge the MP2 interaction energy for a much smaller volume/computational cost, e.g. with a reduction factor of approximately 3 to 4 against other schemes for the NH 3 dimer test system. In addition, it has been found that the MP2c energies of all systems considered herein can be extrapolated at large Ω according to