MICA: Activation Checkpointing for Double-Backward Training of Machine Learning Interatomic Potentials

Conservative machine learning interatomic potentials (MLIPs) predict potential energy and obtain atomic forces as the negative gradient of energy with respect to atomic positions. Computing forces requires a backward pass from energy to atomic positions, and backpropagating the force loss differentiates through this pass, creating double-backward execution. This execution creates two activation classes with different lifetimes: forward activations and first-backward activations. Heterogeneous atomic graph batches make their memory footprint input dependent, while standard checkpointing mainly targets forward activations and does not directly manage first-backward activations. Therefore, we present MICA, an activation checkpointing planner for double-backward execution in conservative MLIP training. MICA combines a checkpoint primitive for double-backward phases with an input-aware dynamic programming planner that selects checkpoint modes for dynamic atomic graph batches under a specified memory budget. Across EqV3, MatRIS, PET, and UMA, MICA's full-checkpoint mode reduces peak memory by 49\% to 86\%, compared with only 10\% to 24\% from standard PyTorch checkpointing. On an 80GB GPU, training EquiformerV3 without checkpointing peaks at 75.47GB and exceeds 50GB in 76.7\% of 1000 iterations, while MICA keeps all 1000 iterations within a 50GB memory budget with 16.25\% step time overhead. Under the same GPU memory capacity, MICA increases the maximum feasible atoms per batch by $4.2\times$ to $9.2\times$. In distributed training, the reduced peak memory allows MICA to reduce reliance on heavier memory saving techniques, such as Fully Sharded Data Parallel (FSDP) and graph parallelism (GP). On a single H100 node with NVLink, MICA trains a MatRIS-MoE model with 2B parameters, achieving a $1.88\times$ to $2.03\times$ speedup over FSDP and GP baselines.