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MOPAC force runs: normal modes are stored in MOPAC's reoriented frame, the structure in the input frame

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#369 2 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
c
Domain
data

Research direction

Start with scripts/parsers/mopac.desc and the MOPAC FORCE output section labeled “ORIENTATION OF MOLECULE IN FORCE CALCULATION”; compare the stored geometry and normal modes in the ch4_force, ch4_geovib, and ch4_force_nothermo fixtures. Adjust the vibration-step data so the geometry and modes share a frame, then check Builder arrows for CH4, H2O, and NH3 MOPAC runs against other codes.

Written by the indexing model from the issue text.

Description

A MOPAC FORCE calculation reorients the molecule ("ORIENTATION OF MOLECULE IN FORCE CALCULATION") and prints its normal modes in that frame, while [GEOMTRACE] in scripts/parsers/mopac.desc stores the input-orientation geometry. The modes ECCE stores therefore belong to a different orientation than the structure they are drawn on.

Found while implementing #367: for CH4 in all three MOPAC fixtures (ch4_force, ch4_geovib, ch4_force_nothermo) the stored modes are not orthogonal to the stored structure's rotations. With the force-orientation geometry the mode symmetries come out right (E, T2, T2, A1, equal to MOPAC's own labels).

Likely effect: the displacement arrows and animation of a MOPAC vibration in the Builder point in the wrong directions (not yet checked by eye). The vibrations table shows MOPAC's own symmetry labels and no Mode description for these runs: #367's analysis detects the mismatch and refuses rather than guess.

Fix: store the geometry the modes belong to, i.e. read MOPAC's force-calculation orientation for the vibration step, or rotate the modes back into the input frame. Then check the Builder's arrows for CH4, H2O and NH3 MOPAC runs against the other codes'.

Dominant language
C
Stars
10
Forks
8
Avg merge
21m
Merged PRs (30d)
1

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