[gmx-users] amber to gromacs conversion of LJ potential

[Chetan Mahajan]

Dear All,

While converting LJ parameters from Amber to Gromacs, acpype tool (that is
used for converting Amber input files into those for gromacs) uses
following form:

sigma = 2 * r * 2^(-1/6)

I understand the factor 2^(-1/6), but there is another "2" that appears in
the beginning. Where is that factor coming from? That factor does not arise
when we choose following forms for LJ potential functions in Amber as well
as Gromacs.

Amber:

[image: Inline image 1]

Gromacs:

[image: Inline image 2]

Thanks in advance!

regards
Chetan