Hello, everyone

Recently, I checked the source code about the “fix spring” in the version of lammps 2001 to help me understand the action induced by this command. However, I am confused by the following codes:

fixcoeff(4,iwhich) = fixcoeff(4,iwhich)*dtfactor*dtfactor (1)

(f_x = k*delx, f_y = k*dely, f_z = k*delz )
( fixcoeff(4,iwhich) = k, kcal/(mol*Å*Å) )

(dtfactor = 48.88821)

I can understand the parameter “dtfactor” which is used to converted the input time unit (fs) to click (that is 1click = 48.88821fs). However, in equation(1), I am not able to understand why the “dtfactor” needs to multiply force constant k twice. I also checked the similar code about the bond style/harmonic, where similar behaviors can not be found.

I really need any help about this question.

Thanks a lot.