Dear Jay,
After about one minute on Google I found this:
http://www.sklogwiki.org/SklogWiki/index.php/9-3_Lennard-Jones_potential
Hope this helps you!
Sincerely,
Christer H. Ersland.
Dear Christer,
Thank you for your link. The reason why I want to find out how the LJ9-3 model in LAMMPS manual is derived because in the manual it says:
LJ93=epsilon((2/15)(sigma/r)^9-(sigma/r)^6)
But if you derive LJ93 directly from LJ12-6 via integration method (also proven by the link you sent), LJ93 should be:
LJ93=(2/3)piepsilonsigma^3((2/15)(sigma/r)^9-(sigma/r)^6)
Comparing the two equations, you realise that the terms (2/3), pi, rho, and sigma^3 are all missing. Therefore I am wondering when I input the value of epsilon in LAMMPS, do I only consider the value of epsilon purely, or do I assume:
epsilon (in LAMMPS LJ93 model) = (2/3)piepsilon*sigma^3
Best regards,
Jay
Let's see what Mark says about this.
Steve