arXiv subjects

Sang Yang

Publications and source records attributed to Sang Yang.

5 recordsLinked to original sources

arXiv2026

Plateau Gaps of Poisson Correctors Encode Metastable Reaction Rates

Metastable reaction rates are commonly inferred from transition-state fluxes, mean first-passage times, or fitted kinetic models. We show that they are directly encoded in the plateau gap of an occupation-time Poisson corrector. For a centered basin-occupation observable, the Poisson corrector develops metastable plateaus in the reactant and product basins, and their separation determines the forward and backward transition rates. This construction requires only the generator, stationary measure, and metastable partition, and therefore does not rely on a predefined transition-state surface. In overdamped and underdamped double-well dynamics, the plateau-gap rate recovers the Kramers, Grote-Hynes, and Pollak-Grabert-H\"anggi hierarchy. The same corrector-martingale decomposition yields a reactive-noise density, revealing where stochastic forcing contributes to transitions in configuration or phase space. Thus, reaction rates and their fluctuation sources emerge from a single corrector field.

cond-mat.stat-mech↗

arXiv2026

Additive-Functional Approach to Transport in Periodic and Tilted Periodic Potentials

In this Letter, we clarify the physical origin of effective transport in periodic and tilted periodic systems. When Brownian dynamics is examined on the scale of a single period, the particle displacement admits a natural separation into a bounded part associated with recurrent motion within the periodic landscape, and an unbounded stochastic part that grows in time and carries the net transport. We show that effective drift and diffusion are governed entirely by this unbounded component, while local potential-induced fluctuations contribute only bounded corrections. Treating the displacement as an additive functional of the stochastic dynamics provides a rigorous formulation of this separation and leads to a corrector-martingale representation at the trajectory level. Within this framework, classical results-including the Lifson-Jackson formula for unbiased periodic systems and the Stratonovich expressions for tilted periodic potentials-follow as direct consequences of the same underlying structure. The same perspective extends naturally to higher-dimensional periodic environments, recovering the standard homogenized transport tensors.

cond-mat.stat-mech↗

arXiv2025

Effective diffusion of Brownian motion in spatially quasi-periodic noise

The effective diffusion of Brownian particles in periodic potential has been a central topic in nonequilibrium statistical physcis. A classical result is the Lifson formula which provides the effective diffusion constant in periodic potentials. Extending beyong periodicity, our recent work [arXiv:2504.16527] has demonstrated that a modified Lifson expression remains valid for Brownian motion in quasi-periodic potentials. In this work, we extend our previous results by incorporating spatial quasi-periodic noise and examining different stochastic interpretations, $\alpha\in[0,1]$. The proposed framework is simple, computationally efficient, and unifies the treatment of diffusion in both periodic and quasi-periodic systems.

cond-mat.stat-mech↗

arXiv2025

Brownian motion and generalized Lifson-Jackson formula in quasi-periodic systems

Brownian motion in periodic potentials has been widely investigated in statistical physics and related interdisciplinary fields. In the overdamped regime, it has been well-known that the diffusion constant $D^*$ is given by the Lifson-Jackson (LJ) formula. With a tilted potential, this model can exhibit giant diffusion. In this work, we start from the basic argument that since any quasi-periodic potential can be approximated accurately using a periodic potential, this formula and the associated physics should also apply to the quasi-periodic potential after some proper redefinition. We derive $D^*$ from the Smoluchowski equation using the fact that its asymptotic solution is a product of a Boltzmann weight and a Gaussian envelope function. Then we analytically calculate $D^*$ in terms of Bessel functions. Finally, we study the giant diffusion with quasi-periodic potentials, generalize the corresponding formula to the condition with tilted potential under the same argument, and calculate $D^*$ analytically. This work generalizes the Brownian motion from periodic potentials to the much broader quasi-periodic potentials, which should have applications in interdisciplinary fields in physics, chemistry, engineering, and life sciences.

cond-mat.stat-mech↗

arXiv2024

Theory of vibrational Stark effect for adsorbates and diatomic molecules

Nowadays the vibrational Stark effect (VSE) of adsorbates at the electrochemical interfaces is generally investigated using the Lambert theory, in which the strong electric field across the interfaces can be treated as some kind of perturbation. Lambert found that the VSE arises mainly from the classical effect, and the quantum effect is negligible. This idea is accepted by almost all current first-principle calculations for this issue. Here we revisit this problem by addressing the fundamental question that to what extent the quantum effect is important for VSE, and if it is observable, then which physical quantity determines this effect. We use the Morse, Lennard-Jones and Dunham potentials as basic potentials to explore this problem using quantum perturbation theory. We define the relative difference between quantum and classical VSE slopes to define the quantum effect, $\eta$, and show that for CO, $\eta \sim $ 2 - 3\%, while for adsorbed hydrogen on Pt electrode, $\eta \sim$ 8 - 10\%, using the experimental data. We find that $\eta$ is determined by the anharmonic coefficient $\chi_e$. Without results we present a new understanding of the VSE as a function of electric field and potential in electrochemical experiments, showing that the nonlinear slope of VSE as a function of potential should arise from the nonlinear relation between electric field and potential across the interfaces, which may resolve the long-standing controversial in experiments.

cond-mat.mtrl-sci↗