Hi every one

I model collision of  two molecules(pyrene) in forcite,and then study the energy transferring process.I  got the result similar to reference under the guidance of Simon and Reinier.However. I find the electrostatic energy have great impact on my result although the value is small to other value.I did four simulations using different electrostatic parameters(the other condition is same.the forcefield is pcff)

(1)the electrostatic interatcion is swiched off.

(2)the summation method is atom based

(3)the summation method is group based( i did not define the charge group,so i think the charge group is calculated automatically,which the hole molecule will be treaded as a charge group)

(4)manully define charge group before collision process,the summation method is group based.

The result is different in (1),(2)and (3)simulation,but the result of (3) is same to (4) simulation,and the reported electrostatic energy is same, too.

my question are

a)Which electrostatic parameters is proper for my case(including switch off the electrostatic interaction)?If possible,please give  a brief explanation about the answer.
b)why the result is same in the (3) and (4)

ps: my version is MS 6.0

Thanks in advance

Sincerely

Li