C4: Evidence-Aware Search for LLM-Guided Materials Discovery

Historical results guide candidate generation in materials discovery, but a limited evaluation budget leaves many directions in the vast composition and structure space rarely or never tried. Search must therefore use successful experience while distinguishing insufficient observation from low potential. We introduce C4, a framework that coordinates four complementary tools: Open expands candidate support, Element identifies promising chemical directions, Explore probes underexplored alternatives, and Refine develops promising parents. C4 combines evaluated outcomes and shared visit records as search evidence, drawing on the exploration–exploitation principle of considering observed returns together with the evidence behind them. An LLM proposes tool-call proportions and branch-scoring weights from structured feedback. The Harness turns these proposals into budgeted calls and concrete substitution choices. Across fourteen multi-property tasks and three seeds with Qwen3-8B, C4 averages 448.33 new feasible compositions, compared with 105.67 for LLEMA, and leads all five baselines in each seed’s total. Component studies and parent reuse illustrate the roles of the tools and their coordination. The advantage also extends to GPT-4o and longer search, while knowledge-guided cases show how additional context redirects the same search process.