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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Peng-Robinson EOS does not appear to load BIPs from Parameters into EquationOfState (or missing docs on correct BinaryRecord format for PR)","articleBody":"Hello again,\n\nPerhaps, I'm misunderstanding what the correct JSON format is for loading Peng-Robinson BIPs now, but prior to v0.9, the correct format was this:\n```\n[\n    {\n        \"id1\": {\n           ...\n        },\n        \"id2\": {\n           ...\n        },\n        \"model_record\": 0.0289\n    }\n]\n```\n\nSeeing as the `model_record` field was dissolved in v0.9, I assumed that the correct format is now the following, though the only information regarding cubic EOS BIPs specifically that I can find is #91:\n```\n[\n    {\n        \"id1\": {\n            ...\n        },\n        \"id2\": {\n           ...\n        },\n        \"k_ij\": 0.0289\n    }\n]\n```\n\nIn any case, whatever field is included is successfully loaded into the `Parameters` object by `Parameters.from_json`, as confirmed by printing the `Parameters` object. The same is true for using `Parameters.new_binary`.\n\nHowever, neither `model_record` nor `k_ij` is successfully loaded into the `EquationOfState` by `peng_robinson = EquationOfState.peng_robinson(params_pr)`. Printing this object's `parameters` attribute produces the following:\n```\nprint(peng_robinson.parameters)\n\n\u003e {'tc': array([190.56, 126.2 ]), 'pc': array([4599000., 3398000.]), 'acentric_factor': array([0.011, 0.037])}\n```\nwith no mention of `k_ij`, which does appear here as a matrix when using another EOS such as PC-SAFT:\n```\nprint(pcsaft.parameters)\n\n\u003e {'m': array([1.    , 1.1879]), 'sigma': array([3.7039, 3.3353]), 'epsilon_k': array([150.03,  90.99]), 'q': array([0.    , 1.1151]), 'k_ij': array([[0.     , 0.03227],\n       [0.03227, 0.     ]])}\n```\n\nFurther evidence that the BIP is not being loaded is given by VLE calculations; results do not change before or after attempting to provide a BIP.\n\nSo, it seems to me that either I am misunderstanding/unaware of the correct way to load Peng-Robinson BIPs now in v\u003e=0.9, or some part of the implementation has broken. I tried to examine the parameter loading source code, but unfortunately I couldn't find the information I'm looking for.\n\nAny advice is appreciated, as always.","author":{"url":"https://github.com/ImagineBaggins","@type":"Person","name":"ImagineBaggins"},"datePublished":"2026-01-22T07:21:09.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/333/feos/issues/333"}