diff --git a/src/REPLICA/bosonic_exchange.cpp b/src/REPLICA/bosonic_exchange.cpp index b5a04c4a43..a58ff97e33 100644 --- a/src/REPLICA/bosonic_exchange.cpp +++ b/src/REPLICA/bosonic_exchange.cpp @@ -381,6 +381,18 @@ void BosonicExchange::spring_force_interior_bead(double **f) const double BosonicExchange::prim_estimator() { + // In the "reduced-beta convention" [e.g. in J. Chem. Phys. 133, 124104 (2010); also J. Chem. Phys. 74, 4078-4095 (1981)], + // the Boltzmann exponents have the form exp[-(beta/P)H], where H is the classical Hamiltonian of the + // ring polymers. This results in a canonical distribution at P times the physical temperature. + // In contrast, the "physical-beta convention" [e.g. in J. Chem. Phys. 99, 2796-2808 (1993)] uses weights of the form exp(-beta*H), + // such that the temperature of the canonical ensemble coincides with the physical temperature. + // Notably, the classical Hamiltonians of the two conventions differ, with the spring constant + // in the reduced-beta convention being P times larger than that in the physical-beta convention. Additionally, the reduced-beta convention + // lacks a 1/P prefactor in front of the external potential. The Hamiltonians of the two conventions are related through + // H_physical = H_reduced / P. Note however that the expressions for the various estimators are unaffected by this choice, + // so as the algorithm for bosonic exchange. The code below was designed to be compatible with both conventions, + // and the choice of convention only affects a single calculation within it. + // Setting the following boolian variable to false amounts to adopting the reduced-beta convention. double convention_correction = (physical_beta_convention ? 1 : 1.0 / np); // Adds the contribution of an interior spring, which is the same as for distinguishable particles.