# electron charge value in dimensionless LJ units

Dear all,

I am using lj units for my simulation and would like to add +e charge (1.602*10^-19 C) on my atoms. What would be the equivalent for this charge in lj units?

From the manual, I could see that the conversion factor is q*=q/(4piperm.vacuumsigmaepsilon)^(1/2) and my system is argon with sigma=3.4 Ang and epsilon being 0.23844 kcal/mole or 1.6566*10^-21 Joule.

Also, by using permittivity of free space value 8.85410^-12 C^2N^-1m^-2, I calculated q as 20.23238.

However, when I add this charge to my system which was initially neutral, the simulation stops running. The problem seems to be from the value of q* I calculated. Could some one tell if I am doing anything wrong while calculating the value of q*?

Thanks,
Ajay

Venkata:

Did you have any negative charges in your system? If not, and you only added positive charges, then you will end up with a system in which all particles are mutually repulsive. Unless your system is really large, this is a Very Bad Idea.

On the other hand, I would have thought that an LJ system would be set up so that a charge of q = 1 corresponds to q = +e. (If this isn’t the case, then perhaps it should be!)

—AEI

Dear all,

I am using lj units for my simulation and would like to add +e charge
(1.602*10^-19 C) on my atoms. What would be the equivalent for this charge
in lj units?

From the manual, I could see that the conversion factor is
q*=q/(4*pi*perm.vacuum*sigma*epsilon)^(1/2) and my system is argon with
sigma=3.4 Ang and epsilon being 0.23844 kcal/mole or 1.6566*10^-21 Joule.
Also, by using permittivity of free space value 8.854*10^-12 C^2N^-1m^-2, I
calculated q* as 20.23238.

However, when I add this charge to my system which was initially neutral,
the simulation stops running. The problem seems to be from the value of q* I
calculated. Could some one tell if I am doing anything wrong while
calculating the value of q*?

if you are already identifying the reduced units
with real units why don't you just use real units
and be happy that you don't have to do any
conversions? i don't see a benefit in using