Different cutoffs

Hi users,

I am setting up immidazolium ionic liquid with water(tip4p model)

Immidazolium force field has non bonded cutoffs of 12 Angstorm ( both lj and coulombic) .

tip4p/ice has lj cutoff of 8.5 Angstorm ( coulombic cutoff has not been mentioned, likely to take the same cutoff 8.5 Angstorm)

how to combine two force fields using pair_style.

thanks in advance
karthik kumar

Hi users,

I am setting up immidazolium ionic liquid with water(tip4p model)

Immidazolium force field has non bonded cutoffs of 12 Angstorm ( both lj and
coulombic) .

tip4p/ice has lj cutoff of 8.5 Angstorm ( coulombic cutoff has not been
mentioned, likely to take the same cutoff 8.5 Angstorm)

how to combine two force fields using pair_style.

you'd have to use pair style hybrid.

but more seriously, how are you going to generate
the mixed force field terms? and what cutoff to use?

axel.

Hi Axel sir,

I am trying to use hybrid style,

pair_style hybrid lj/cut/coul/long 12.0 lj/cut/coul/long/tip4p 8.5

but leading to an error two sub- pair_styles should have same coulombic cutoffs.

can you please suggest me in this regard… can’t i have different coulombic cutoffs for different sub-styles.

  1. I want mixed terms to evaluate with lj/cut/coul/long
    For mixed terms cutoffs may be 12 Angstrom.

Thanks a lot in advance

karthik

Hi Axel sir,

I am trying to use hybrid style,

pair_style hybrid lj/cut/coul/long 12.0 lj/cut/coul/long/tip4p
8.5

but leading to an error two sub- pair_styles should have same coulombic
cutoffs.

can you please suggest me in this regard... can't i have different coulombic
cutoffs for different sub-styles.

it *doesn't matter*. both styles are using kspace
and thus the 'effective' cutoff is infinity in any case.
you can safely set the coulomb cutoff for both
potentials to the same value.

axel.

If you read the doc page for lj/cut/coul/long you will see that
you can specify the LJ and Coulomb cutoffs independently
for each pair of atom types. You don't need pair_hybrid
for that.

Steve