Iterated Denoising Energy Matching for Sampling from Boltzmann Densities
Tara Akhound-SadeghJarrid Rector-BrooksAvishek Joey BoseSarthak MittalPablo LemosCheng-Hao LiuMarcin SenderaSiamak RavanbakhshGauthier GidelYoshua Bengio
Proposes an iterative, simulation-free score matching algorithm that trains diffusion samplers directly from unnormalized energy functions without data or MCMC, achieving up to five times faster training and successfully scaling to the challenging 55-particle Lennard-Jones system.
Sampling from unnormalized probability distributions, known as Boltzmann distributions, is a foundational challenge in computational chemistry, physics, and materials discovery. In these physical systems, determining the equilibrium states of molecular and particle systems requires exploring complex, high-dimensional energy landscapes. Traditional numerical techniques such as Markov Chain Monte Carlo and Molecular Dynamics are computationally expensive and scale poorly to high dimensions. While recent deep learning generative models offer an alternative, existing methods either require pre-existing data samples, rely on restrictive model architectures, or require computationally demanding trajectory simulations during training that prevent scaling to larger systems.
The article introduces and evaluates Iterated Denoising Energy Matching (iDEM), a neural sampling framework designed to learn directly from a system's energy function and its gradients without requiring any prior training data. The primary objective is to demonstrate that iDEM can efficiently scale to high-dimensional physical systems while outperforming existing neural and flow-based samplers in both sample quality and computational efficiency.
The approach operates via a bi-level iterative scheme that combines a diffusion-based model with an off-policy replay buffer. In the inner loop, a neural network is trained using a simulation-free score matching objective that estimates target score directions through local Gaussian perturbations directly on the energy function. In the outer loop, the updated diffusion model generates candidate states to populate a replay buffer without computing costly backpropagation gradients through the simulation. This iterative feedback loop smooths the rugged energy landscape and allows the model to explore multiple isolated modes effectively. The framework was evaluated across synthetic multimodal distributions and physical particle benchmark systems ranging up to 165 dimensions, incorporating physical geometric symmetries.
The evaluation yielded several key findings regarding speed, scalability, and sample accuracy. First, iDEM achieved convergence between two to five times faster than leading alternative frameworks, reducing training times by approximately a factor of four on high-dimensional benchmarks. Second, iDEM demonstrated state-of-the-art sample quality across standard metrics, including superior negative log-likelihood, mode coverage, and effective sample size. Third, iDEM was the first energy-trained neural method capable of scaling to the challenging 55-particle Lennard-Jones system, whereas competing diffusion-based neural samplers failed to converge or experienced catastrophic divergence. Finally, analysis confirmed that the error in the internal score estimator primarily impacts the magnitude rather than the direction of the score vectors, which can be stabilized in practice through simple gradient clipping.
These results demonstrate that simulation-free score matching can substantially reduce computational overhead while mitigating mode-collapse issues in scientific machine learning. By eliminating the need for expensive trajectory integration during parameter updates, organizations can dramatically lower compute costs and shorten experimental timelines for molecular design, protein modeling, and materials simulation.
Organizations developing computational sampling pipelines should consider adopting bi-level, simulation-free energy matching frameworks when scaling up molecular and atomic simulations. Future development should focus on integrating adaptive variance-reduction techniques into the score estimator and exploring faster numerical solvers for the outer-loop generation step to further optimize training throughput.
While iDEM demonstrates robust performance, key limitations include the statistical bias inherent in finite Monte Carlo score estimation within sparse or low-density regions of the energy landscape, as well as the requirement of having access to analytically computable energy gradients. Nevertheless, the empirical stability across high-dimensional tasks supports strong confidence in the framework's effectiveness for unnormalized density sampling.
- Paper: Denoising Diffusion Probabilistic Models, Jonathan Ho et al. (2020). Its denoising diffusion probabilistic model establishes the reverse-noising framework that iDEM repurposes for sampling energy-defined Boltzmann distributions.
- Paper: Score-Based Generative Modeling through Stochastic Differential Equations, Yang Song et al. (2021). Its SDE and score-based account grounds the diffusion sampling machinery iDEM adapts to learn a sampler from an energy function rather than data.
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