[zain]

Hey guys
the question is quite simple what will the the Z+/Z- be?. i mean theres relative charges like +1 and -1... or will it be in coulombs?
Many thanks, Zain

[Yggdrasil]

Relative charges.  Note that in the numerator of the equation, you have an e² term which converts the Z+ and Z- to actual values of charge.

In general, Z will be used to refer to relative charges, while q will be used to refer to the absolute value of charge.

[zain]

many thanks

[zain]

one more question
what is the born exponent?

[Alpha-Omega]

n =Born repulsion exponent (integer depends on VSE configuration, varies from 5 to 12).  n, the Born exponent is specific to each ion - for a lattice the values of the cation and anion are averaged.

[zain]

i think i understand.
for example what would it be for LiF?

[Alpha-Omega]

Check This Link:  http://www.wiredchemist.com/chemistry/data/born_exponent.html

And read this paper-short and to the point...:  http://database.iem.ac.ru/mincryst/glasser.pdf 
reference Pg. 3 and 4.