def METHOD_NAME(self, atomcoords_index: int = -1) -> float:
    """Return the nuclear repulsion energy."""
    nre = 0.0
    atomcoords = convertor(self.data.atomcoords[atomcoords_index], "Angstrom", "bohr")
    for i in range(self.data.natom):
        ri = atomcoords[i]
        zi = self.data.atomnos[i]
        for j in range(i+1, self.data.natom):
            rj = atomcoords[j]
            zj = self.data.atomnos[j]
            d = np.linalg.norm(ri-rj)
            nre += zi * zj / d
    return convertor(nre, "hartree", "eV")