elastic constants for lipid bilayer


I want to compute area expansion modulus for a phospholipid bilayer. I have been guided by the scripts from folder ELASTIC. But because I use an orthogonal box, I get:

ERROR: Cannot change box tilt factors for orthogonal box

On mailing list I saw a suggestion: “You need to add dummy box tilt factors (with a value of 0) to your initial structure, so that it is considered as a triclinic box.In your structure file, you should therefore have this line after the xlo xhi ylo yhi zlo zhi lines :
0.0 0.0 0.0 xy xz yz.”

So if I add this line, I get:
ERROR: KSpace style does not yet support triclinic geometries

If I don’t use Kspace, I get:

ERROR: Pair style requires a KSpace style …/pair_lj_sdk_coul_long

The KSpace I am using is

kspace_style pppm/cg 1.0e-5 1.0e-6

I am using lammps version


Is there something else I could change, or elastic constants cannot be calculated for a membrane using the modified scripts from ELASTIC? (I changed the files init.mod and potential.mod accordingly).

Thank you,

pppm/cg does not support triclinic cells but both ewald and pppm do. Just use one of the above ones.