Merge pull request #605 from RandomDefaultUser/density_cube_reading_fix

Made a density read from a cube file a 4D array as well

mala/targets/density.py

@@ -417,6 +417,7 @@ def read_from_cube(self, path, units="1/Bohr^3", **kwargs):
                 "We recommend to check and change the requested units"
             )
         data, meta = read_cube(path)
+        data = np.expand_dims(data, -1)
         data *= self.convert_units(1, in_units=units)
         self.density = data
         self.grid_dimensions = list(np.shape(data)[0:3])