Operator File Generation¶
The operator file is the central input file of an MCTDH calculation. It provides a mathematical representation of the molecular Hamiltonian by combining the vibrational degrees of freedom with the electronic states and their vibronic couplings.
Unlike electronic structure packages such as GAMESS or Gaussian, which calculate molecular energies and properties, MCTDH requires the Hamiltonian to be written explicitly in a format that can be interpreted by the propagation algorithms. The operator file serves as this bridge between electronic structure calculations and quantum dynamics simulations.
For vibronic Hamiltonians, the operator file contains the vibrational frequencies, diabatic electronic energies, interstate electronic couplings, and the linear and quadratic vibronic coupling constants that describe how the electronic states interact with the nuclear motion.
Role of the Operator File¶
The operator file defines every term appearing in the Hamiltonian used throughout an MCTDH calculation.
These include
- Vibrational kinetic energy operators
- Harmonic potential energy terms
- Diabatic electronic state energies
- Interstate electronic couplings
- Linear vibronic coupling terms
- Quadratic vibronic coupling terms
Together, these quantities completely define the vibronic Hamiltonian that governs the time evolution of the nuclear wavepacket.
Workflow¶
The operator file is generated after obtaining the vibronic coupling parameters from electronic structure calculations.
Reference Geometry
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Normal Mode Analysis
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Distortions Along Normal Modes
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Electronic Structure Calculations
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Curve Fitting
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Selection of Active Vibrational Modes
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Operator File Generation
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Wavepacket Propagation
The first five steps are used to determine the parameters required for the vibronic Hamiltonian. Once these quantities have been obtained, they are assembled into the MCTDH operator file, which can then be used for wavepacket propagation or Hamiltonian diagonalization.
Automatic Operator Generation¶
Constructing an operator file manually can be tedious, especially for systems containing many vibrational modes and several electronic states.
To simplify this process, we developed an automated workflow consisting of
- a Bash script (
operator-make.sh), which collects all required data and assembles the operator file, and - a Fortran program (
operator.f90), which formats the vibronic coupling parameters into the syntax required by MCTDH.
Together, these programs automatically generate a complete operator file from the fitted vibronic coupling data.
What You Will Learn¶
In this section, we will cover
- the prerequisites required before operator generation,
- preparation of the necessary input files,
- the Bash script used to automate the process,
- the supporting Fortran program,
- and the structure of the generated MCTDH operator file.
By the end of this tutorial, you will be able to automatically construct an operator file that is ready for MCTDH wavepacket propagation and Hamiltonian diagonalization.
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Download Operator
Complete Operator used in this tutorial.
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Bash script
Complete bash script used for operator generation.
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Fortran Code
Fortran code used in bash script
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Fitting Parameters
Fitting parameters of one of the vibrational modes used in operator file
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Frequency File
Frequency file containing vibrational data
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Ground State Diabatisation Log file
Gamess output of Ground state diabatisation