I try to compute the unit cell energy of the Ti2CO2 MXene with NWchem.
Computing the 1x1 supercell with 4x4x1 K-points grid I got -1875 Ha.
Computing the 2x2 supercell with 2x2x1 K-points grid I got -7502 Ha, that means -1875.5 Ha per unit cell.
I understand, that for useful results convergence should be reached with K-points and the basis set. But here I just want to understand the source of the 0.5 Ha discrepancy. Previously I thought, that NxM supercell is equivalent to NxM K-points grid. Apparently it is not true. What is the source of such a significant difference?
Inputs for both cases are attached.
I also have asked this question in StackExchange Materials Modelling group here. But for a while there are no decisive answers.
It looks like you’re trying to use the Gaussian DFT code in NWChem. This code does not contain periodic boundary conditions. Only the plane-wave band code in the nwpw module can do periodic dft calculations with k-points.
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