mmffstbn.par was missing the class-2 stretch-bend entry for atom
types (2,2,2) (sp2 carbon center with both bonds BT-flagged) that
is present in the original MMFF94 parameter set. Without it,
class-2 C(sp2)-C(sp2)-C(sp2) angles fall through to the MMFFDFSB
default (0.30/0.30) instead of the fitted values (0.219/0.250).
Verified against an independent transcription of the original file
(Tinker's mmff94.prm): it is the only missing entry among 283,
with no value differences in the rest. Energy impact on the
Halgren validation suite (JIYJAC): stretch-bend 0.2368 kcal/mol vs
0.1858 from the original BatchMin program; matches to 4 decimals once the entry is restored.
Inserted after the class-1 (2,2,2) entry to preserve the canonical
CXBA ordering.
Fixes#3003
Billy Wayne McCann, PhD.
bed9812e15
