charge on the surface

[nasimanousheh]

@jadhao and @kadupitiya

• In inhouse, the same as lammps, we can define charge (between zero to -0.01 C.m-2) on surface.
• We can compare the potential energy results of inhouse (4th column) with lammp (8 column (epair) instead of 7 column (pe)).
• Since I added more columns in energy outputs in lammps, in next PR, I will update the examples for uncharged surface and README.
• The factor 4 hasn't changed yet. It will be in next PR.
• In this PR, I didn't change the code for uncharged surfaces. The result for uncharged surface is remained unchanged.

[jadhao]

@nasimanousheh uncharged case works good with lammps and house. next I suggest sending only the factor 4 vs. 16 change, and updating examples for both uncharged and charged cases. charged case not tested.