ANT Home Page
A Molecular Dynamics Program for Performing
Classical and Semiclassical Trajectory Simulations for Electronically Adiabatic
and Nonadiabatic Processes for Gas-Phase and Materials Systems
Jingjing Zheng, Zhen Hua Li, Ahren W.
Jasper, David A. Bonhommeau, Rosendo Valero, Rubén Meana-Pañeda, Steven L. Mielke, Linyao Zhang, Zoltan Varga, and Donald G. Truhlar
Department of Chemistry and Supercomputing Institute
University of Minnesota, Minneapolis,
Most recent version: 2020
Date of most recent version: September 15, 2020
Date of most recent manual update: January, 12 2022
ANT ("Adiabatic and Nonadiabatic
Trajectories) is a Fortran 90 molecular dynamics program. It has the following
ANT can be used for dynamics governed either
by a single potential energy surface (electronically adiabatic processes) or by
two or more coupled potential energy surfaces (electronically nonadiabatic
- For an electronically adiabatic process,
there are two options: (1) the user can supply a potential energy surface as a
subroutine or (2) the code can calculate direct dynamics in which energies and
gradients are obtained directly from electronic structure calculations carried
out with the Gaussian09, Molpro, or MOPAC-mn electronic structure
package (which must be obtained separately).
- For a nonadiabatic process the user must supply two or more surfaces and their
couplings in analytic form as subroutines or may employ adiabatic or diabatic
input for direct dynamics. Electronically nonadiabatic processes can be treated
in either the adiabatic or diabatic representation by a variety of methods
including surface hopping by the fewest switches with time uncertainty (FSTU)
algorithm, FSTU with stochastic decoherence (FSTU/SD), the Ehrenfest
method, and coherent switches with decay of mixing (CSDM). When one uses
the electronically adiabatic representation, the user may either provide the adiabatic
surfaces and nonadiabatic couplings by direct dynamics, or the program may
calculate them from the diabatic surfaces and diabatic couplings, which may
either be analytic or direct.
- The army ants tunneling algorithm is implemented for both electronically adiabatic and electronically nonadiabatic trajectories on unimolecular reactions or any other unimolecular process. For electronically nonadiabatic processes, the army ant tunneling algorithm is only implemented for mean-field methods, e.g., CSDM and SE methods. The tunneling path can be along any of the valence internal coordinates or a combination of two stretch coordinates.
- ANT can handle reactive trajectories, inelastic collisions, and unimolecular
processes. It can calculate cross sections and rate constants.
- ANT can be run at fixed energy or for
thermal ensembles. Collision processes between an atom
and a diatom can be carried out by special algorithms with a more advanced
treatment of the initial conditions. Another option is that one may
begin trajectories at a dividing surface passing through a saddle point. A
limited set of final-state analysis options is available.
- Three methods (TRAPZ,
mTRAPZ, and mTRAPZ* methods)
are available to ensure zero-point energy maintenance in classical trajectory
- The program can handle periodic conditions if a periodic
potential is given.
- The program can also calculate steepest-descents paths.
- ANT can use general initial conditions for polyatomic bimolecular or unimolceular processes, or it can use accurate WKB initial conditions for atom-diatom or diatom-diatom collisions.
The current version of ANT has a large suite of
test runs to assist the user in setting up the program and understanding the
One can run ensembles of classical trajectories (also called molecular
dynamics) on a single user-supplied potential energy surface or on coupled
surfaces; the latter is called electronically nonadiabatic dynamics or
non-Born-Oppenheimer dynamics. Several non-Born-Oppenheimer (multi-surface)
trajectory methods are available, including:
Surface hopping methods
- Coherent Switches with Decay of Mixing (CSDM)
[ J. Chem. Phys, 121 (04), 7658 (2004),
J. Chem. Theor. Comput., 1 (05), 527 (2005) ].
- Self Consistent Decay of Mixing (SCDM)
[ J. Chem. Phys, 120 (04), 5543 (2004) ].
- Semiclassical Ehrenfest (SE, aka TDSCF).
- FSTU with Stochastic Decoherence (FSTU/SD)
[ J. Chem. Phys, 127, 194306 (2007)]
- Fewest Switches with Time Uncertainty (FSTU)
[ J. Chem. Phys, 116 (02), 5424 (2002),
Chem. Phys. Lett., 369 (03), 60 (2003) ].
- Tully's Fewest Switches (TFS)
[ J. Chem. Phys, 93, 1061 (1990) ].
Several prescriptions for preparing the initial conditions are also available:
- Quasiclassical state selection.
- Quasiclassical thermal ensemble.
- Classical thermal ensemble.
- User-supplied initial conditions.
- Thermal ensemble.
- User-supplied initial conditions.
Thermal ensembles may be controlled by various thermostats (Berendsen,
Anderson, or two-chain Nosé-Hoover) and/or a Berendsen barostat.
There are options for geometry optimization, normal mode analysis, and
For single-surface dynamics, the user must supply a subroutine that calculates
the potential energy surface and its gradient.
For multi-surface dynamics, the user must supply a subroutine that calculates
the coupled diabatic potential energy surfaces, their scalar couplings, and
the gradients of the surfaces and couplings. However the coupled-surface
dynamics may be carried out in either the diabatic or adiabatic representation;
in the latter case the program calculates the adiabatic surfaces and their
coupling vector due to nuclear momentum by starting with the diabatic
information in the user-supplied subroutine. This option is available for an
arbitrary number of states.
Sample potential energy surface routines, including gradients, are available in
the POTLIB library.
ANT platform compatibility
The ANT code has been tested successfully on the following
Itasca and Mesabi Linux Clusters
Intel FORTRAN Compiler 2018.0.128
Licensing and downloading:
ANT - version 2020 is licensed under the Apache License, Version 2.0.
The manual of ANT - version 2020 is licensed under CC-BY-4.0.
Publications of results obtained with the ANT - version 2020 software should cite the program and/or the article describing the program.
No guarantee is made that this software is bug-free or suitable for specific applications, and no liability is accepted for any limitations in the mathematical methods and algorithms used within. No consulting or maintenance services are guaranteed or implied.
The use of the ANT - version 2020 implies acceptance of the terms of the licenses. The software may be downloaded here.
Links to other pages of interest
Computational Chemistry at the University
Department of Chemistry at the University
This document last modified on August 2, 2021
Updated by: Software Manager