how can I able to add columbic interactions alongside REBO POTENTIALS?
how can I able to add columbic interactions alongside REBO POTENTIALS?
technically, it is easy to add explicit coulomb to any potential via pair style hybrid/overlay.
but in practice, that is a very tricky thing to do. REBO already includes a complete description of the interactions between carbon and hydrogen, and that also includes coulomb interactions in an effective manner. so how would you avoid double counting and thus getting complete garbage as a result?
TLDR answer: you cannot without a LOT of work (programming and model development and testing).
axel.
Dear Dr.Kohlmeyer
As far as I know, REBO potential does not include clumbic and vdw interactions. Also, AIREBO includes vdw interactions but it does not include colombic interactions.
Best
reza
how can I able to add columbic interactions alongside REBO POTENTIALS?
technically, it is easy to add explicit coulomb to any potential via pair style hybrid/overlay.
but in practice, that is a very tricky thing to do. REBO already includes a complete description of the interactions between carbon and hydrogen, and that also includes coulomb interactions in an effective manner. so how would you avoid double counting and thus getting complete garbage as a result?
TLDR answer: you cannot without a LOT of work (programming and model development and testing).
axel.
Dear Dr.Kohlmeyer
As far as I know, REBO potential does not include clumbic and vdw interactions. Also, AIREBO includes vdw interactions but it does not include colombic interactions.
that is a massive oversimplification, and this doesn’t conflict with what i have been telling you. while there are no explicit coulomb terms, they are included implicitly on the short range. same for AIREBO. and same for van der Waals. if you look closely at the way how the the Lennard-Jones term is included in AIREBO, you see, that it uses a switching function, that smoothly adds LJ interactions to only compute their contributions for longer ranging interactions. that way, there is no double counting of the LJ interactions at short range.
as i was saying, if you simply add a coulomb potential to either REBO or AIREBO, you will double count the coulomb contributions at short range. so if you want to turn REBO (or AIREBO) into a potential that supports long-range coulomb interactions AND becomes polarizable through considering charge equilibration, you will have to write/derive a modified version, that does not double count those interactions, considering the complexity of AIREBO, that is a massive undertaking.
that is what i was trying to tell you and there is nothing more that i have to add to this.
axel.
thanks for your good guides. so, when I add QEQ to AIREBO potential, in fact I add coloumbic interaction of all atoms to my simulation? or QEQ only effects on charge equilibrium of short-range interactions (As you said).
In other words,by using AIREBO potential, I want to ask that QEQ command effects on long-range and short-range coloumbic interactions or effects only on short-rang colombic interactions?
thanks
Dear Dr.Kohlmeyer
As far as I know, REBO potential does not include clumbic and vdw interactions. Also, AIREBO includes vdw interactions but it does not include colombic interactions.
that is a massive oversimplification, and this doesn’t conflict with what i have been telling you. while there are no explicit coulomb terms, they are included implicitly on the short range. same for AIREBO. and same for van der Waals. if you look closely at the way how the the Lennard-Jones term is included in AIREBO, you see, that it uses a switching function, that smoothly adds LJ interactions to only compute their contributions for longer ranging interactions. that way, there is no double counting of the LJ interactions at short range.
as i was saying, if you simply add a coulomb potential to either REBO or AIREBO, you will double count the coulomb contributions at short range. so if you want to turn REBO (or AIREBO) into a potential that supports long-range coulomb interactions AND becomes polarizable through considering charge equilibration, you will have to write/derive a modified version, that does not double count those interactions, considering the complexity of AIREBO, that is a massive undertaking.
that is what i was trying to tell you and there is nothing more that i have to add to this.
axel.
thanks for your good guides. so, when I add QEQ to AIREBO potential, in fact I add coloumbic interaction of all atoms to my simulation? or QEQ only effects on charge equilibrium of short-range interactions (As you said).
no, i did not say that. this is incorrect in multiple ways.
In other words,by using AIREBO potential, I want to ask that QEQ command effects on long-range and short-range coloumbic interactions or effects only on short-rang colombic interactions?
no. you are not making any sense. neither REBO nor AIREBO will pay any attention to the value of the charge assigned with an atom.
at this point, please do the smart thing and read the rebo/airebo paper and understand how this potential works. …and you probably need to learn some more about potentials in general, as your statements about QEQ are missing the point by a large margin, too.
it is pointless to continue discussing without you knowing what you are talking about.
axel.
I know about REBO or AIREBO but I dont know about QEQ command actions.
AIREBO has 3 segment REBO+VDW+TORSION that VDW adding with switching function for accomodating with REBO segment and considering long-rand interactions.
I want to know, by using QEQ command, add I coloumbic interactions to my simulations totally?
I use AIREBO potentials with QEQ command, what is diffrence with using QEQ command and without using QEQ command?
you said me before that " i can use QEQ with AIREBO but practically, it makes no sense. " why?
thanks-reza
thanks for your good guides. so, when I add QEQ to AIREBO potential, in fact I add coloumbic interaction of all atoms to my simulation? or QEQ only effects on charge equilibrium of short-range interactions (As you said).
no, i did not say that. this is incorrect in multiple ways.
In other words,by using AIREBO potential, I want to ask that QEQ command effects on long-range and short-range coloumbic interactions or effects only on short-rang colombic interactions?
no. you are not making any sense. neither REBO nor AIREBO will pay any attention to the value of the charge assigned with an atom.
at this point, please do the smart thing and read the rebo/airebo paper and understand how this potential works. …and you probably need to learn some more about potentials in general, as your statements about QEQ are missing the point by a large margin, too.
it is pointless to continue discussing without you knowing what you are talking about.
axel.
I know about REBO or AIREBO but I dont know about QEQ command actions.
you may know about them, but most certainly do not know enough of how they actually work.
AIREBO has 3 segment REBO+VDW+TORSION that VDW adding with switching function for accomodating with REBO segment and considering long-rand interactions.
I want to know, by using QEQ command, add I coloumbic interactions to my simulations totally?
obviously not. QEQ does not add anything to the potential function. all it does is modify charges according to the chosen algorithm.
as mentioned before (but as i have now well documented, that you are not enough paying attention), you would have to use pair style hybrid/overlay to add a potential interaction to an existing potential. however, in the case of REBO/AIREBO, this would - as i have also pointed out repeatedly - lead to double counting of interactions and thus garbage results.
I use AIREBO potentials with QEQ command, what is diffrence with using QEQ command and without using QEQ command?
none. make a test and see for yourself.
you said me before that " i can use QEQ with AIREBO but practically, it makes no sense. " why?
if neither REBO, nor AIREBO pay any attention to charges, where is the meaning of modifying those charges with QEQ? there is none!
with an MD code as modular and flexible as LAMMPS, there are many things you can technically do, but that have no physical meaning or are bound to result in complete garbage. or a completely ineffectual.
at this point you have exhausted my patience.
please refrain from continuing this discussion until you have spend some time thinking about what i was telling you and have properly read (and re-read) my responses.
axel