Molecular dynamics (Mac OSX user): what software can I use to plot RDFs for NPT simulations? VMD only works for NVT (constant volume) I would be very grateful if someone could recommend a way to plot RDFs for NPT ensemble molecular dynamics simulation results.  

I use CP2K to run NVT simulations and usually use VMD to process results, but I don't see a way in VMD to deal with NPT results, where the volume is different at each time step.  I'm hoping that someone can recommend a piece of software that can deal with my CP2K output (i.e., a position file in terms of atomic xyz coordinates and a file that contains volume output) on a Mac or Linux system.

I have spent several hours online looking for a solution, but haven't even come across discussions of this problem.  This seems odd so maybe I'm using the wrong search terms.  If anyone can point me to online discussions of this issue, that would be great.  

I'm also not having much luck tagging this question!  If anyone knows of any molecular dynamics-related tags I could use to reach people or perhaps of a more appropriate StackExchange site, I would welcome any suggestions.  Thank you.
Thank you, Buck, for all your suggestions.  You're right that a good way to check the influence of the volume is to try varying it.  I did that by using the maximum and minimum volumes of the fluctuations in one simulation.  There was some variation, so the volume does matter!

I was lucky enough to hear about "travis," an amazingly simple-to-compile code (even for Macs) available online for free.  I thought I'd share that information here because other people are bound to run into this same problem.  This code, travis, takes my trajectory file and my volume file and then asks a number of questions interactively.  It outputs a nice CSV file that can be plotted.

Thanks again for your help, Buck.  Really helped me think this through.  I'd like to ask the moderators or whoever is in charge of tagging to please add some molecular dynamics-related tags if possible!  Thank you.