Adjoint Sampling: Highly Scalable Diffusion Samplers via Adjoint Matching
Aaron J. HavensBenjamin Kurt MillerBing YanCarles Domingo-EnrichAnuroop SriramDaniel S. LevineBrandon M. WoodBin HuBrandon AmosBrian Karrer
Introduces a scalable stochastic optimal control framework that trains diffusion samplers from unnormalized densities with dramatically fewer expensive energy evaluations, enabling efficient amortized molecular conformer generation.
Sampling from complex physical distributions using unnormalized energy functions is a fundamental challenge across computational chemistry, physics-based inference, and molecular modeling. Existing techniques—such as Markov Chain Monte Carlo, flow models, and diffusion samplers—struggle with high dimensions or require extensive evaluations of expensive physics-based energy calculations at every gradient step. The article introduces Adjoint Sampling, an on-policy variational inference framework based on stochastic optimal control that trains continuous diffusion samplers using unnormalized energy functions without requiring pre-existing ground truth data.
The main objective of the article is to demonstrate that Adjoint Sampling enables scalable, highly efficient sampling by decoupling model optimization from costly energy evaluations and trajectory simulations. The approach leverages a modified training objective called Reciprocal Adjoint Matching combined with an experience replay buffer. Instead of simulating full trajectories and computing energy gradients during every parameter update, the algorithm stores final states and their energy gradients, reconstructing intermediate states via exact analytical formulas. The methodology incorporates physical symmetries and periodic boundary conditions using equivariant neural networks, evaluating performance on synthetic physical potentials (such as 55-particle Lennard-Jones systems) and large-scale molecular conformer generation across thousands of organic molecules from the SPICE and GEOM-DRUGS benchmarks.
The findings show that Adjoint Sampling significantly reduces computational overhead while maintaining superior sample accuracy. On synthetic multi-particle systems, the method achieves competitive geometric distance metrics while reducing energy function evaluations per gradient update by several orders of magnitude compared to prior score-matching approaches. In molecular conformer generation benchmarks, Adjoint Sampling consistently outperforms standard industry baselines such as RDKit in coverage recall across varied structural complexities. When combined with standard post-generation relaxation, pretrained Cartesian Adjoint Sampling attains 96.65% recall coverage on SPICE and 87.01% on GEOM-DRUGS, substantially exceeding classical rule-based methods.
These results imply that high-fidelity molecular conformer generation and physical simulation can scale effectively without ground-truth structural training sets, reducing computational costs and turnaround times in drug discovery and material design workflows. Practitioners should consider adopting Adjoint Sampling for large-scale molecular conformation pipelines, utilizing torsional models when fast unrelaxed sampling is required and pretrained Cartesian models when highest recall after structural relaxation is prioritized. However, users should note that the framework targets unnormalized energy approximations whose reliability depends on the underlying energy potential, requiring standard relaxation and validation steps before making downstream experimental decisions.
- Paper: Adjoint Matching: Fine-tuning Flow and Diffusion Generative Models with Memoryless Stochastic Optimal Control, Carles Domingo-Enrich et al. (2025). Adjoint Sampling’s reciprocal adjoint objective builds directly on this paper’s Adjoint Matching framework, making its control-based training method essential context.
- Paper: Iterated Denoising Energy Matching for Sampling from Boltzmann Densities, Tara Akhound-Sadegh et al. (2024). This earlier energy-based diffusion sampler provides the closest comparison for understanding how Adjoint Sampling changes training to reduce costly energy evaluations.
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