Hi all

I am trying to simulate fluid flow through Carbon Nanotubes using LAMMPS. the problem i am facing now is that, while using KSPACE solver there is a restriction - cannot use pppm/ewald in non periodic dimensions. but in my simulation only the flow direction can be made periodic, the other two must be non periodic. is there a method to overcome this restriction?

it would be really helpful if you could give your suggestions on this issue.

Thanking you in advance…

unni

Hi all

I am trying to simulate fluid flow through Carbon Nanotubes using

LAMMPS. the problem i am facing now is that, while using KSPACE solver

there is a restriction - cannot use pppm/ewald in non periodic

dimensions. but in my simulation only the flow direction can be made

periodic, the other two must be non periodic. is there a method to

overcome this restriction?

can you please explain,

why you need kspace at all

for that kind of system?

axel.

Dear Axel

I am trying to simulate water flow through carbon nanotubes. I beleive that inorder to study such a system we have to consider the long range electrostatics. Also in all the literatures related to this problem they have used pppm.

Unni

Dear Axel

I am trying to simulate water flow through carbon nanotubes. I beleive that

inorder to study such a system we have to consider the long range

electrostatics. Also in all the literatures related to this problem they

have used pppm.

i think in this case using long range electrostatics are overrated.

i would just use a long coulomb cutoff and one of the smooth

damping schemes for it.

your flow shoud add enough noise to your average water

density distribution structure that any residual effects from

the lack of long-range electrostatics will be negligible.

on the other hand you have to consider that with a 3d ewald/pppm,

you have unphysical periodic contributions to your forces.

what i would consider to implement is a cutoff scheme, that

considers only the one periodic direction for the cutoff.

that would reduce any cutoff artefacts significantly.

axel.

You can use periodic boundary conditions in all directions, and try

increasing the box size in the directions normal to the flow (hence

increasing the distance between the periodic images of your CNT), and

see if the properties you're trying to measure converge.

It is not possible to use long range electrostatic with only one

periodic dimension, and clearly all previous works on water flow

through CNT have in fact considered a periodic array of CNT, although

it is not always explicitely mentionned in the papers.

The standard procedure when only one dimension is not periodic is to

articificially increase the box size in that direction, typically a

factor of 3 with regards to the physical system is used (see the doc

page for kspace_modify slab option), so you can use that as a starting

point in the two directions normal to the flow...

Best regards,

Laurent

thank you Axel & Joly for your valuable suggestions…

unni