Fix bug: make the energy got by vasprun.xml same as OUTCAR
For more please see about issue 916 I am not sure it is a bug or a feature... But I think the results of 'get_potential_energy()' should be the same between vasprun.xml and OUTCAR
For more please see about issue 916 I am not sure it is a bug or a feature... But I think the results of 'get_potential_energy()' should be the same between vasprun.xml and OUTCAR