WIP: Investigate mbeef
As described in #265 (closed), there might be a problem in the mgga_x_mbeef functional form. This is the one that's in the MBEEF paper; the MBEEF-vdw paper actually has the minus sign...
As described in #265 (closed), there might be a problem in the mgga_x_mbeef functional form. This is the one that's in the MBEEF paper; the MBEEF-vdw paper actually has the minus sign...