Calculating pressure in polymer lattice simulations

We propose several novel methods for calculating the bulk pressure in polymer lattice simulations. Our first method combines chain insertion/deletion with Wang–Landau – Optimized Ensemble sampling in the space of number of chains n, which is very efficient and accurate at low to intermediate polymer volume fractions ϕ (e.g., ≲0.7). We then propose two methods in canonical-ensemble simulations to efficiently and accurately calculate the bulk pressure at high ϕ where chain insertion/deletion becomes inefficient. Finally, combining these methods leads to complete thermodynamics over the entire range of continuous and exact ϕ-values with negligible finite-size effects. We also analyze in detail the error caused by the cut-off in n-space.