QM/MM with point charge equal to zero problem

Questions
#1

Hello,
I am recently using Q-CHEM to carried out QM/MM calculations, and I have some point charges with zero charge. Just like this:
-8.51710727 -3.96383986 -1.96067631 0.00000000
-8.48687774 -3.91199616 -1.96727712 0.00000000
-8.69900583 -4.09370930 -2.04906479 0.00000000
-8.47654720 -4.83214256 -2.36147128 0.00000000

After the calculation, I found that the forces on these point charges are not zero as I checked the efield.dat file. The results are:
0.00009224266 0.00000713111 -0.00019090695
0.00009510766 0.00000809305 -0.00019357297
0.00008696419 0.00000482941 -0.00017600281
0.00008841079 0.00001597472 -0.00015747707

So I don’t know if there is something wrong with my input file or there is something I need to take care of.
Any suggestions are appreciated.
Thanks in advance.

#2

The efield.dat file contains electric field vectors for each point charge. To obtain the force, electric field is multiplied by the charge. Zero charge will yield zero force.

1 Like
#3

Thank you very much.
This has confused me a lot.