# Set charge with using qeq/dynamics

Dear all,

I would like to change the charge of structure (say, electrode) from 0 charge to -10 charge.
I also want to use qeq/dynamics to calculate charge of each carbon/hydrogen of electrode.

I know that if i just put -10 charge onto electrode, qeq will calculate charge.
But, I want to change the charge of electrode slowly, for 1 ns (?).
I found that “set charge” can change the charge of specific type of atom.
so, i am assuming i can modify the charge by using like :

variable dC equal ramp(0, -10) : total charge need to be divided with number of atoms in electrode.
set type 6 7 charge v_dC
fix 1 electrode qeq/dynamic 1 10 0.001 100 param.qeq

would be possible ?
can i change the system’s charge, and qeq can simultaneously read that changes ?

Thanks,
Sungwon

Dear all,

I would like to change the charge of structure (say, electrode) from 0 charge to -10 charge.
I also want to use qeq/dynamics to calculate charge of each carbon/hydrogen of electrode.

I know that if i just put -10 charge onto electrode, qeq will calculate charge.
But, I want to change the charge of electrode slowly, for 1 ns (?).
I found that “set charge” can change the charge of specific type of atom.
so, i am assuming i can modify the charge by using like :

variable dC equal ramp(0, -10) : total charge need to be divided with number of atoms in electrode.
set type 6 7 charge v_dC
fix 1 electrode qeq/dynamic 1 10 0.001 100 param.qeq

would be possible ?

i don’t think that the charge equilibration fixes can handle charged systems correctly (or systems that are being gradually charged or discharged) the documentation warns against it and i believe there have been multiple discussions on the subject in the past, so please check out the mailing list archives for more information.

axel.

If you mean apply a voltage to a system (between electrodes for example)
and have QEq assign charges while including that effect, then that
is an altered version of QEq. Stan (Ccd) is working on a version that does that.

Steve