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name: atom-site-swap description: >- Propose Na/X (or configured) lattice-site swaps to lower the relaxed energy of a fixed-composition configuration. Use when optimizing site occupancy in Agenticoptimizer, reading energy feedback, or choosing which atoms to exchange.

Atomistic site-swap agent

Goal

Find a low-energy arrangement of species on the lattice sites at a fixed composition (ratios from config.toml). This replaces genetic-algorithm operators: you choose which sites to swap.

Do not change the number of each species. Only permute occupations on lattice sites.

Domain rules

1. Lattice sites come from swap_params.lattice_sites (e.g. all Na positions in the supercell).
2. Allowed species are swap_params.atom_swaps (e.g. Na and X).
3. X means a vacancy. It is removed before relaxation; do not invent other elements.
4. Composition must stay at swap_params.ratio (e.g. [0.66, 0.34] → ~66% first species, ~34% second).
5. Framework atoms (everything that is not a lattice site) are fixed — never swap them.
6. Lower relaxed total energy is better. Prefer swaps that break unfavorable clustering or improve mixing when energy stalls.

How to propose a move

Each step you receive:

• current occupancy as a list of symbols, one per lattice site index 0 .. N-1
• current energy (eV) and recent history
• counts of each species (must be preserved)

Respond with only a JSON object (no markdown fences, no commentary):

{"swaps": [[i, j], [k, l]], "rationale": "short reason"}

• Each [i, j] exchanges the species on sites i and j.
• Prefer 1–4 swaps per step; more is allowed if justified.
• Only swap pairs that currently have different species (otherwise the move is a no-op).
• Site indices must be in range and refer to lattice sites only.

If you believe the current configuration is optimal enough to stop:

{"swaps": [], "done": true, "rationale": "why stop"}

Strategy hints

• Early: diversify — break large same-species clusters; sample different local arrangements.
• Mid: exploit — refine neighborhoods that previously lowered energy.
• Late: small local swaps only; stop when energy no longer improves for several steps.
• Never propose a move that changes species counts.
• Avoid repeating an occupancy that already appears in the history.

What you must not do

• Do not change cell size, framework chemistry, or the target ratio.
• Do not request DFT settings changes mid-run; relaxation params come from config.
• Do not output prose outside the JSON object.