[Nishant Sharma (Nishant1600)]

Fixes #177 (the args_dict mutable-default part).

Problem

MatterSimCalculator.__init__ and the deprecated MatterSimCalculator.load() declare args_dict: dict = {} and store the argument directly as self.args_dict. On the legacy graph path, calculate() writes into that dictionary:

self.args_dict["batch_size"] = 1
self.args_dict["only_inference"] = 1

As a result:

• every calculator created with the default shares one dictionary, so running one calculator changes the args_dict of all the others (the reproduction in [Bug]: Mutable defaults bug and global variables #177);
• a dictionary passed in by the caller is mutated in place.

Fix

• Default args_dict to None in both signatures.
• Store a private copy: dict(args_dict) if args_dict is not None else {}.

The values the calculator passes to build_dataloader are unchanged.

Tests

tests/forcefield/test_calculator_args_dict.py adds two regression tests using the existing mattersim_potential_cpu and si_diamond fixtures:

• test_default_args_dict_is_not_shared: two default calculators; using one leaves the other's args_dict empty.
• test_caller_args_dict_is_not_mutated: a caller-supplied dict keeps its contents after a calculation.

Validation

Windows 11, Python 3.12, CPU-only torch:

• The new tests fail on main (2 failed) and pass with this change.
• pytest tests/forcefield/test_calculator_args_dict.py tests/forcefield/test_calculator_flags.py tests/forcefield/test_calculator_pickle.py: 16 passed.
• black --line-length 88, isort --profile black and flake8 --max-line-length=88 --ignore=E203,W503 (the pre-commit settings) pass on the changed files.

The full test suite was not run, and CUDA/MPS were not tested.

Not in this PR

#177 also notes that Potential.__init__ sets torch.backends.cuda.matmul.allow_tf32 globally. That is a behavioural design choice (scoping it per computation), so I left it for a separate change.

🤖 Generated with Claude Code

[Nishant Sharma (Nishant1600)]

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