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Charge Group Issues for Montmorillonite

Dear Colleagues, 
Greetings, 

Please HELP! I am working on "Sorption" module simulations for MMT removal of heavy metals. However, for more than three weeks now I am trying to fix the group charge issue I am facing. I have tried uff, clayff and modified uff. I keep getting this message when I calculate the charges from "Modify" tool: 

"No charge groups have been calculated.
The particles that are being considered for a charge group are not charge neutral.
The absolute net charge is 15.9955 and it should be less than 0." 

What could be the issue? 
The file is attached herewith. 
Regards, 
Hamzah 
Best Answer chosen by HH
reinierreinier
Hi Hamzah,

Your structure contains Na+ ions. They cannot be contained in a charge group, since charge groups must be charge neutral. Likewise the framework is charged and cannot be partitioned in neutral groups.

You will need to set Electrostatic summation method to "Ewald". This method can handle charged systems, in the sense that it will add a charge-neutralizing background.

Regards,
Reinier

All Answers

reinierreinier
Hi Hamzah,

Your structure contains Na+ ions. They cannot be contained in a charge group, since charge groups must be charge neutral. Likewise the framework is charged and cannot be partitioned in neutral groups.

You will need to set Electrostatic summation method to "Ewald". This method can handle charged systems, in the sense that it will add a charge-neutralizing background.

Regards,
Reinier
This was selected as the best answer
HHHH
Many Thanks Reinier, this was really helpful