[lammps-users] How to set different weighting coefficients for different atom pairs

Hi, all

I am simulating dynamics of a peptide on a TiO2 surface in water. Amber force field was adopted to represent the peptide, so I think I should use “special_bonds amber” to turn off the pairwise interaction for all pairs of atoms (atoms in water and peptide) bonded to each other or separated by 2 bonds. But the surface was hydroxylated TiO2, there was angle bending terms for the Ti-O-H (Ti-hydroxyl O-hydroxyl H), the hydrogens can electrostatically interact with the Ti atoms to which they are connected through the angle. So I need to turn on the Coulombic interaction for Ti-H pair. How can I set different weighting coefficients for different atom pairs? That is, how can I turn off the 1-3 Coulombic interaction for the peptide and water, but turn on the Coulombic interaction for the Ti-H pair?

Many thanks.

Chunya

2011/1/31 wuchunya <[email protected]>:

Hi, all

I am simulating dynamics of a peptide on a TiO2 surface in water. Amber
force field was adopted to represent the peptide, so I think I should use
“special_bonds amber” to turn off the pairwise interaction for all pairs of
atoms (atoms in water and peptide) bonded to each other or separated by 2
bonds. But the surface was hydroxylated TiO2, there was angle bending terms
for the Ti-O-H (Ti-hydroxyl O-hydroxyl H), the hydrogens can
electrostatically interact with the Ti atoms to which they are connected
through the angle. So I need to turn on the Coulombic interaction for Ti-H
pair. How can I set different weighting coefficients for different atom
pairs? That is, how can I turn off the 1-3 Coulombic interaction for the
peptide and water, but turn on the Coulombic interaction for the Ti-H pair?

you cannot.

well, not without changes to the sources. you are mixing-and-matching
different force fields. that that is always a problem.

the way i imagine this could be implemented, would be through
writing a custom pair style that only works on atoms that are
excluded via special bonds and then uses a different set of
special_coul/special_lj scaling factors as needed and
add those interactions via hybrid/overlay to the system.

not very elegant or efficient.

cheers,
    axel.