Hi, guys

who can tell me what kind of correction method is used in Lammps for finite cutoff distance?

Hi, guys

who can tell me what kind of correction method is used in Lammps for finite cutoff distance?

none - unless you specify it - e.g. you can use pair modify tail to

get LJ tail correction

if you like. Also pair_modify offset.

Also some of the pair styles like lj/smooth do a smoothing

at the cutoff.

Steve

Does LAMMPS support damping shift force method (Gezelter’s method) to calculate the electrostatics ?

Thanks.

Guozhen

I don't know what it is, so probabliy not. It is

an alternative to PPPM or Ewald. Is so, what

is the difference?

Steve

According to the DL_POLY2 manual, Gezelter’s method is an Damped Shift Force Coulomb sum which truncates the 1/r potential at rcut, adds a linear term to the potential in order to make both the energy and the force zero at the cutoff and furthermore introduce an additional “damping” function to moderate the 1/r dependence. It was eported to be a viable alternative to the Ewald summation.

(http://jcp.aip.org/resource/1/jcpsa6/v124/i23/p234104_s1)

Guozhen

According to the DL_POLY2 manual, Gezelter's method is an Damped Shift Force

Coulomb sum which truncates the 1/r potential at rcut, adds a linear term to

the potential in order to make both the energy and the force zero at the

cutoff and furthermore introduce an additional "damping" function to

moderate the 1/r dependence. It was eported to be a viable alternative to

the Ewald summation.

(http://jcp.aip.org/resource/1/jcpsa6/v124/i23/p234104_s1)

what you describe sounds similar to the damped coulomb

in either CHARMM or GROMACS. there also is the (generalized)

reaction field method (i have a half-ready implementation of that

somewhere on my laptop) that follows similar assumptions.

it certainly is not a viable alternative to ewald summation in a general

context. particularly, if you have an inhomogeneous distribution of the

charge density (e.g. at a phase boundary) in your system, using a

shifted force method will incur a spurious potential along the inhomogeneity.

even a 3d-ewald can lead to (smaller) problems in extreme cases

and a 2d-ewald sum might be required.

the test systems in all publications on "approximate" long-range

electrostatic methods that i have seen over the last ~15 years all

use systems that are - expectedly - most likely to show a minimal

impact. so i would strongly recommend to do careful testing before

applying any of those methods for systems, that are not as forgiving.

i would love to see anything of them use a "hard" problem for a change.

i know from colleagues that do simulations, e.g., on lipids, that even

for lipids with zwitterionic head groups, you would need either a small

ewald or pppm correction or a massive increase of the coulomb cutoff

(with damping) to get the correct behavior for the pure lipid in water.

once you use ionic lipids with counterions, you _have_ to use proper

treatment of long-range electrostatic (i.e. ewald, PPPM, (S)PME, or FMM)

or else your results will be wrong.

cheers,

axel.