gcmc for mixtures of molecules


I would like to run a gcmc for a mixture of two molecules, water tip4p and a small molecule with three atoms.

My first idea was to define two molecules and use shake for constrainning the geometry.

However, it is not possible to have to fix shake in a single simulation.

Can I use a fix shake for water and a fix rigid for other molecule in a single molecule?

Also, the manual says that use of two fix gcmc may be problematic if using template molecules. However, I do not fully understand what you mean by: “An existing template molecule will need to be referenced by the user for each subsequent fix gcmc command.” Does these mean that this can not be done at all? Or that there is a way to define the template so the first fix does not delete the template for the second fix gcmc? I am sorry, but I find this sentence confusing.

Thank you very much in advance for your advice?

Best regards,


The reason for the confusion is that the code is constructed in a way that makes sense for standard problems, without consideration for questions like “what happens if their are two different SHAKE molecules?” or “what happens if there are two different GCMC molecules.” After the code is written, we attempt to document which non-standard problems can and can not be handled. In some cases, the only way to find out is to run your own tests.

One way to eliminate all of these difficulties is to run fix gcmc with translation/rotation, but without any dynamics.