Dresden 2026 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 54: Statistical Physics: General II

DY 54.10: Talk

Thursday, March 12, 2026, 17:30–17:45, ZEU/0114

Perturbative projection of many-body systems with applications in enhanced sampling of biomolecules — •Joan Salas-Llabrés — Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany

Using a modification of the well-known Mori-Zwanzig projection operator formalism, a Generalized Langevin Equation (GLE) is derived for a general observable of interest that only depends on the phase space positions, from a many-body Hamiltonian in the presence of a constant linear external potential. In particular, the friction memory kernel is analytically computed, and via an operator perturbative expansion, it is expanded in terms of the external potential up to first order in the potential strength. We name this approach ``perturbative projection", and it allows to see the effects that this bias can have on the effective dynamics of a reaction coordinate, in particular on its friction. To test the obtained analytical expression and thus compare to some order of approximation the change in friction with direct results, we choose the conformational dynamics of alanine nonapeptide in water, obtained via molecular dynamics simulations. The results show agreement over a range of bias strengths. This provides new insight into the effects of an external bias on the dynamics of a system of interest, pointing to its fundamental nature in the level of its Hamiltonian, and which in particular has important consequences for the analysis of results coming from enhanced sampling techniques.

Keywords: Projection operators; Generalized Langevin Equation; Effective dynamics; Friction; Polypeptide