I am currently performing mechanical simulations using Geometry Optimization (Forcite Module) in Materials Studio, and I am applying three different force-fields: PCFF, Dreiding and Compass. I need to perform the simulations at atmospheric pressure, however I am not sure if I should include a value of 0.0001013 GPa (i.e. atmospheric pressure) for external pressure in the Forcite Geometry Optimization dialog box, or whether the force-fields are already parameterized to perform the simulations at atmospheric pressure, i.e. should I leave the external pressure as zero?

Does anyone have any idea?

Thanks for your help!