OPLS-AA

OPLS-AA
Name	OPLS-AA
Developer	William L. Jorgensen
Initial release	1996
Latest release	2001
Programming languages	Fortran, C
License	academic/research
Application	molecular dynamics, Monte Carlo
Influences	AMBER (force field), CHARMM

OPLS-AA OPLS-AA is an all-atom classical force field developed for molecular modeling of organic liquids, biomolecules, and materials. It provides a transferable set of bonded and nonbonded parameters to simulate conformational energetics and thermophysical properties with applications spanning Yale University research groups, industrial ExxonMobil studies, and academic collaborations. The model has been integrated into software packages maintained by groups at University of California, San Diego, Rutgers University, and Stanford University for use in studies ranging from small-molecule hydration to protein folding.

History and Development

OPLS-AA traces origin to parameter sets published by William L. Jorgensen and collaborators in the early 1990s, building on prior work in molecular simulation at institutions such as Bell Labs and DuPont. Early motivation drew on comparative benchmarks against contemporaneous force fields like AMBER (force field) and CHARMM, and experimental datasets from repositories curated by National Institute of Standards and Technology researchers. Development proceeded through iterative fitting to reproduce conformational energies, liquid densities, and heats of vaporization measured at facilities including Brookhaven National Laboratory and published in journals associated with the American Chemical Society. Subsequent expansions and refinements involved collaborations with computational chemistry groups at Columbia University, University of Minnesota, and Massachusetts Institute of Technology.

Force Field Description and Functional Forms

The functional form of the force field uses standard classical terms familiar to practitioners trained with implementations at Los Alamos National Laboratory and Lawrence Berkeley National Laboratory: bonded stretching, angle bending, torsional Fourier series, and nonbonded van der Waals plus Coulombic interactions. The nonbonded van der Waals form employs the Lennard-Jones 12-6 potential, a form also used in AMBER (force field) and CHARMM parameterizations developed at University of North Carolina at Chapel Hill. Electrostatic interactions are treated with fixed partial charges assigned by fitting to quantum chemical data from computations performed with software developed at IBM Research and methods promoted by Gaussian, Inc. practitioners. Long-range electrostatics in periodic systems are typically computed using Ewald summation techniques refined in collaborations with computational teams at Princeton University and ETH Zurich.

Parameterization and Atom Typing

OPLS-AA adopts an all-atom atom-typing scheme that differentiates environments such as aliphatic, aromatic, heteroatom-bound, and conjugated centers—strategies informed by spectroscopic and ab initio studies at Harvard University and California Institute of Technology. Parameter values were derived from fits to high-level quantum mechanical potential energy surfaces obtained from methods developed at Cornell University and University of Oxford, and from condensed-phase observables measured at laboratories including Argonne National Laboratory. Torsional parameters use Fourier series coefficients chosen to reproduce rotational barriers characterized in work by groups at Imperial College London and University of Cambridge. Charge distributions draw on electrostatic potential fitting techniques advanced by researchers associated with Max Planck Society institutes.

Validation and Performance

Validation efforts compared predicted properties—liquid densities, enthalpies of vaporization, free energies of solvation—against experimental benchmarks from databases curated at National Institutes of Health and measurement programs at European Molecular Biology Laboratory. Performance assessments reported in publications from teams at University of California, Berkeley, University of Illinois Urbana-Champaign, and Scripps Research showed that OPLS-AA often matches or improves upon structural predictions relative to force fields developed at University of Groningen and University of Pennsylvania for certain classes of organics. In protein and peptide modeling, comparative studies involving groups at University of Zurich and University of Tokyo highlighted strengths in conformational energetics and limitations in reproducing some backbone ensembles when compared to newer polarizable models from Sandia National Laboratories and Argonne National Laboratory.

Applications and Use Cases

OPLS-AA has been applied to a wide range of systems: small-molecule solvation and partitioning studied by researchers at Pfizer and GlaxoSmithKline; ligand binding and virtual screening projects run by groups at Novartis and Roche; membrane simulations investigated by teams at University of British Columbia and Karolinska Institutet; polymer and materials modeling pursued at MIT and Delft University of Technology; and mechanistic studies in enzymology conducted by labs at ETH Zurich and Cold Spring Harbor Laboratory. It has also supported methodological developments in free energy methods used by practitioners at University of Cambridge and high-throughput workflows developed at Lawrence Livermore National Laboratory.

Limitations and Extensions

Limitations of the force field include fixed-charge approximations and a lack of explicit electronic polarizability, issues also noted in comparisons with polarizable force fields from University of Chicago and Oak Ridge National Laboratory. Extensions and refinements have aimed to address these gaps: hybrid parameters and reparameterizations for specific chemotypes produced by teams at University of California, San Diego and Rutgers University; integration with ab initio based correction schemes explored at Argonne National Laboratory and Barcelona Supercomputing Center; and implementations combined with enhanced sampling algorithms developed by groups at Max Planck Society and Weizmann Institute of Science. Active community contributions from academic and industrial laboratories continue to adapt the parameter set for emerging challenges in drug discovery, materials science, and biophysics.

Category:Force fields