{"paper":{"title":"FastChem 4: New chemical elements and improved convergence behaviour","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"","cross_cats":["astro-ph.IM","astro-ph.SR"],"primary_cat":"astro-ph.EP","authors_text":"A. Beate C. Patzer, Daniel Kitzmann, Joachim W. Stock","submitted_at":"2026-05-18T12:00:07Z","abstract_excerpt":"Chemical equilibrium calculations are a key ingredient for modelling and interpreting spectroscopic observations of (exo)planets, brown dwarfs, cool stars, and protoplanetary disks. As these applications increasingly probe non-solar elemental abundances and previously underrepresented elements, equilibrium chemistry solvers must be both numerically robust and capable of handling complex chemical systems. Here we present FastChem 4, a major update to the open-source FastChem equilibrium chemistry code. We extend the gas-phase solver with a multidimensional Newton-method that mitigates the slow "},"claims":{"count":0,"items":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"2605.18264","kind":"arxiv","version":1},"verdict":{"id":null,"model_set":{},"created_at":null,"strongest_claim":"","one_line_summary":"","pipeline_version":null,"weakest_assumption":"","pith_extraction_headline":""},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2605.18264/integrity.json","findings":[],"available":true,"detectors_run":[{"name":"ai_meta_artifact","ran_at":"2026-05-19T23:33:35.254500Z","status":"skipped","version":"1.0.0","findings_count":0},{"name":"claim_evidence","ran_at":"2026-05-19T23:21:58.968190Z","status":"completed","version":"1.0.0","findings_count":0}],"snapshot_sha256":"724e6f0eb801598a688d9ba3539db1f693c06b1f343cd4a5516022b4aa2b3dd6"},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}