Examination of numerical accuracy on fragment-DFT calculations with integral values of total electron density functions

Fragment molecular orbital (FMO) method gives a powerful tool to investigate electronic structures for biological substances, and ABINIT-MP program has been developed to implement ab initio FMO calculations effectively. We introduced DFT code into ABINIT-MP and applied fragment-DFT (F-DFT) calculations to model polypeptides. The total accuracy of numerical integrations employed in those calculations was examined by the total numbers of electrons in the molecules. It is shown that the numerical integral of the total density function under the fragment approximation works as an indicator for the numerically total accuracy on the F-DFT implementation.