[lammps-users] change kspace style on restart

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1

Dear LAMMPS users,

When I attempt to read a restart file from a simulation that used kspace_style ewald (or pppm), but change the pair_style to one which does not use kspace (setting kspace_style to none), I receive the following error: “ERROR: Pair style is incompatible with KSpace style.” The input script is show below, where meoh.rst used lj/charmm/coul/long pair_style. In my application, I am using a custom pair_style I developed to post-process which doesn’t require kspace, but the pair_style ‘lj/charm/coul/charmm’ experiences the same problem.

I attempted to get around this problem by converting the restart file to a data file, however, the data file loses too much precision to be an accurate representation of the simulated ensemble (for example, energy and pressure are too different). So I need a way to use the binary coordinates.

One solution I considered is to convert my custom pair_style to a compute. It was much simpler to edit a pair_style when developing the post-processing calculation, because there wasn’t a compute that was similar to what I wanted to calculate. It seems to me that it would be easier to suppress the kspace style when reading a restart, than to convert the custom pair_style to a compute.

Thank you,

Harold Hatch

units real

neigh_modify delay 0 every 1 check yes

atom_style full

bond_style harmonic

angle_style charmm

dihedral_style charmm

pair_style lj/charmm/coul/charmm 8.0 9.0

pair_modify mix arithmetic

kspace_style none

read_restart meoh.rst

special_bonds charmm

2

How about changing the pair style and kspace style after reading in the restart file.

Paul

3

Dear Paul,

Thank you for the suggestion. I seemed to have understood this problem wrong, because read_restart actually doesn’t read anything about the kspace style, as I saw in the manual. So if I change the order like you mentioned as below:

4

You’re welcome. I meant that you specify the old pair style before, then read the restart file, then specify the new pair style. You’ll have to respecify the pair coeffs.

Paul

5

You're correct that LAMMPS stores no info about KSPACE
settings in the restart file. So you have to re-specify them
in your input script. And they will have to be compatible
with whatever pair style you have defined when the
run begins.

Steve