2026-06-22 Model Chemistry Step, Metadata Protocol, and MOPAC/xTB via MDI

Goal

As the previous plan 2026-06-19 was developed it became clear the direction needed substantial changes. This is the result of the knowledge, adding a Model Chemistry Step modeled after and eventually replacing the Forcefield Step; providing the MDI capabilities using metadata accesses via Stevedore; and finally the actual MOPAC & xTB MDI implementations.

Supporting MDI with, initially, MOPAC and xTB as engines for LAMMPS. This will allow us to use semiempirical methods with MD. This initial phase will build on the work with the MDI connections for MLFFs, starting with standalone tests and ending with incorporating the functionality in the LAMMPS step in SEAMM.

Contents:

• Plan: Model Chemistry Step, Metadata Protocol, and MOPAC/xTB via MDI
  • Overview
  • The _model_chemistry dictionary
  • The metadata protocol
  • Worked implementation: MOPAC
  • Worked implementation: xTB
  • How lammps_step consumes this
  • Phased plan
  • Open questions carried into this plan
  • References
• Phase A – MOPAC-side MDI engine launch contract and port strategy
  • Scope
  • Why Option C (script shipped in data/)
  • Division of responsibility
  • The two new classmethods
  • Launch script shape (driver-side, Phase B)
  • Port allocation
  • Method-set guard test
  • Open questions
  • References
• Phase B – Model Chemistry Step (selection + storage)
  • Scope
  • Confirmed SEAMM mechanics
  • The _model_chemistry contract
  • Open decisions
  • Grammar (delivered)
  • Next steps (pending D1-D4)
  • References
• Phase C – LAMMPS consumption of the model chemistry (MDI)
  • Scope
  • What already exists in lammps_step
  • Decisions (locked)
  • Proven by-hand invocation
  • Contracts consumed
  • Implementation steps (lammps_step)
  • run_mdi.sh template
  • Open risks (low now)
• Phase D (sketch) – Forcefield handling folded into Model Chemistry
  • Goal
  • Type vocabulary
  • Provider (decision: DU1 = (b))
  • KEY OPEN ISSUE – atom-type assignment
  • Consumer pattern
• Project handoff – LAMMPS + MOPAC QM-MD coupling via MDI
  • 1. What this project is
  • 2. Working conventions (please honor these)
  • 3. Key SEAMM mechanics (verified in source)
  • 4. Phase A – MOPAC MDI engine launch contract (DONE, released)
  • 5. DevOps CI modernization (DONE)
  • 6. Phase B – Model Chemistry Step (IN PROGRESS)
  • 7. Phase C – LAMMPS consumption (NOT STARTED)
  • 8. Open questions / watch list
  • 9. File map