This project provides a Bash-based interface that connects the ABIN molecular dynamics (MD) engine (ABIN repository) with the ChemShell QM/MM framework. It automates the exchange of structures, energies, and gradients between the two programs, allowing hybrid quantum–classical molecular simulations to run seamlessly.
ABIN performs classical or mixed quantum–mechanical/molecular–mechanical (QM/MM) dynamics. ChemShell computes quantum energies and gradients using external quantum chemistry engines such as MNDO, ORCA, MOLPRO and others.
The interface:
- Reads atomic coordinates from ABIN’s temporary files.
- Converts them into ChemShell input format.
- Executes the selected QM code.
- Extracts energies and gradients from the output.
- Returns them to ABIN for the next MD step.
This transformation is fully automated in Bash.
CHEMSHELL_INTERFACE/
├── CHEMSH/
│ └── r.chemsh # Interface for ground-state MD (ABIN standard mode)
├── CHEMSH-LZ/
│ └── r.chemsh-lz # Interface for non-adiabatic MD (ABIN LZ mode)
├── SetEnvironment.sh # Environment setup for ABIN and QM codes
└── .gitignore
r.chemsh — couples ChemShell to ABIN for ground-state molecular dynamics.
It transfers geometries, calls the quantum engine (MNDO or ORCA), and returns energies and gradients for each MD step.
r.chemsh-lz — adapts the interface for non-adiabatic (Landau–Zener) dynamics,
where ABIN propagates multiple electronic states and changes its file-exchange pattern.
This version reads state information and prepares corresponding ChemShell/MOLPRO inputs.
The interface is executed automatically by ABIN when placed in the appropriate directory for the calculation.
ABIN calls the interface script as:
./r.chemsh $timestep $ibeadParameters of the calculation can be adjusted in chemsh.inp or chemsh-lz.inp, depending on which interface is used. The interface can also generate atomic connectivity automatically if required by the selected force field.