I have a problem you want to get help

I simulated adsorption calculated by towhee code

I use Gibbs Ensemble

I calculated the methane adsorption in porous materials

I use 2 combined force field is: Dreiding and Trappe-UA

When running I got the following error:

molecule type 2 only has one atom.

CBMC regrow can not do for one unit molecule

(My second molecule is CH4)

However, I can not increase the number of atoms up, because molecules of CH4 in Trappe-UA forcefield is an atom CH4

Looking forward to the answers!

Mr. Ha

Here's a description of methane

trappe-ua methane

input_style

'basic connectivity map'

nunit

1

nmaxcbmc

1

lpdbnames

F

forcefield

'TraPPE-UA'

charge_assignment

'manual'

unit ntype qqatom

1 'CH4' 0.0d0

vibration

0

improper

0

 

Response：

Well, you haven't posted the moves part of your input file but I guess you are using Configurational-bias 2 box molecule Transfer move. Since your molecule is only one (united) atom big, in fact configurational bias regrowth into another box is meaningless, and that's exactly what the code complaints. You should instead use Center-of-Mass Molecule Translation Move. As your molecule is a single (spherical) unit, rotation is meaningless as well and all you need is translation, that is from one box to another. CBMC moves are designed to simulate adsorption of long chained (or branched), big molecules into the tunnel-like formation of the porous adsorbents. They try to regrow the molecule right into the shape of the tunnels it will be inserted into. Otherwise the molecules will almost never fit into the tunnels with their current form using simple translation and rotation moves and the MC simulation will not advance. But as your system is very simple you really do not need such a complex algorithm. Just transfering your units to the other box will be sufficient.