扩散模型可精确模拟分子动力学,无需力场与轨迹数据
Diffusion Models are Molecular Dynamics Simulators
- 用扩散采样器模拟朗之万动力学,每步对应一个随机微分方程的积分
- 仅需静态构型训练,生成轨迹具类分子动力学时间相关性
- 精度由模型能力与采样步数控制,适用于无显式力场场景
我们证明,带有批量维度顺序偏置的去噪扩散采样器等价于过阻尼朗之万动力学的欧拉-马鲁雅姆积分器。每个反向去噪步骤及其对应的弹簧刚度,可视为一个随机微分方程的有效时间步长,该步长由噪声调度与刚度共同决定。学习到的得分函数扮演漂移项角色,即学习能量的梯度,从而在扩散采样与朗之万时间演化之间建立精确对应。这一等价关系将分子动力学重构为扩散模型形式。精度不再依赖固定且极小的MD时间步长,而是由两个可扩展的调控参数控制:模型容量(决定漂移近似精度)和去噪步数(决定积分器分辨率)。实践中,这形成一个完全数据驱动的分子动力学框架,仅从不相关的平衡构型中学习作用力,无需手工设计力场,也不需要轨迹数据进行训练,同时仍保持与学习能量相关的玻尔兹曼分布。我们推导了轨迹级、信息论意义上的误差界,清晰分离离散化误差与得分模型误差,阐明温度通过有效弹簧引入,并证明所生成采样器能产生具有类分子动力学时间相关性的轨迹,尽管模型仅在静态构型上训练。
原文摘要 · Abstract (English)
We prove that a denoising diffusion sampler equipped with a sequential bias across the batch dimension is exactly an Euler-Maruyama integrator for overdamped Langevin dynamics. Each reverse denoising step, with its associated spring stiffness, can be interpreted as one step of a stochastic differential equation with an effective time step set jointly by the noise schedule and that stiffness. The learned score then plays the role of the drift, equivalently the gradient of a learned energy, yielding a precise correspondence between diffusion sampling and Langevin time evolution. This equivalence recasts molecular dynamics (MD) in terms of diffusion models. Accuracy is no longer tied to a fixed, extremely small MD time step; instead, it is controlled by two scalable knobs: model capacity, which governs how well the drift is approximated, and the number of denoising steps, which sets the integrator resolution. In practice, this leads to a fully data-driven MD framework that learns forces from uncorrelated equilibrium snapshots, requires no hand-engineered force fields, uses no trajectory data for training, and still preserves the Boltzmann distribution associated with the learned energy. We derive trajectory-level, information-theoretic error bounds that cleanly separate discretization error from score-model error, clarify how temperature enters through the effective spring, and show that the resulting sampler generates molecular trajectories with MD-like temporal correlations, even though the model is trained only on static configurations.
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