Dear Andrew
I checked with fix deform command removed but I am getting same error again. That means its not with fix deform command. But the same script is working fine with npt ensemble.
Well, in that case it is important for you to figure out what exactly is different between the two scripts. From the sound of it, you are using a fix that wants a pressure somewhere but it is not being calculated, but it is impossible to say without an input script.
Dear all,
Thank you for your support. My issue was solved after I changed the fix print command output. I matched it with thermo output step. Now It works fine. But isnt it strange that same script worked fine with npt and not with nvt. Now it works with both. I dont know whether its a bug or not.
Probably it worked with fix npt because fix npt has to calculate the pressure at each time step anyway, whereas without the pressure is only calculated each time thermo output is printed.
Dear Paquay
You are right this is the actual reason. Thank you for your response.