LJ truncate+shift


I’m new to GULP. I’m trying to do something simple with a truncated and shifted LJ potential, but I only seem to get raw truncation. My understanding is that adding “energy” or “ener” to the “lennard” option should result in the truncated and shifted potential, i.e.,

lennard epsilon zero energy

(Full example input file pasted below. When I generate a binding curve, there’s clearly a jump at r = 5 Angdtrom.) I cannot figure out how to get the expected behavior. Any advice greatly appreciated.

Best wishes,

Input file:

lj binding curve file
20.0 20.0 20.0 90.000000 90.000000 90.0
Al core 0.000000 0.000000 -1.50
Al core 0.000000 0.000000 1.50
library Al.lib

Library file:

Al core 0.0
lennard epsilon zero energy
Al core Al core 1.0 2.0 0.0 5.0

Hi Steve,
I’ve just had a quick try with essentially your input file and I see the energy go to zero at 5.0 Angstroms as expected. Can you confirm that you are using the latest version of GULP 6.0?

Hi Julian,

Thanks for your quick reply!

OK, I was using GULP 5.1 (and working from that manual). I played around with GULP a couple of years ago but the project got put on the back burner, and simply used the code I’d already downloaded. I guess I wasn’t expecting much to have changed wrt LJ and point charges!

Using GULP 6.0 gives the expected behavior.


Hi Steve,
Apologies for that - there was a bug at one stage that crept in and it seems you hit it with your old version. Glad to hear that updating the code fixes things.
Best regards,