Its full name shows that Optimized Potentials for Liquid Simulations (OPLS) is a set of molecular force fields suitable for molecular dynamics of liquid systems, and has a wide range of applications in the field of simulation computing of small organic molecules and protein condensed phases. The OPLS force field is specially developed for liquid systems such as peptides, proteins, nucleic acids, organic solvents, etc. It is generally applicable to the water model of Tip3P or TIP4P. The OPLS force field is currently used in many mainstream computing software packages. Through the OPLS force field, Alfa Chemistry can offer customers MD simulation services.
Fig 1. A set of non-bonding parameters was developed within an all-atom-optimized liquid analog potential (OPLS-AA) force field to simulate concentrated electrolyte solutions of anionic surfactants. (Abdel-Azeim S, et al. 2020)
Two sets of force fields are included in OPLS: OPLS-AA (all-atomic force field) and OPLS-UA (joint atomic force field, not considering hydrogen atoms). However, the OPLS-AA all-atomic force field is typically employed nowadays.
The functional form of the OPLS force field is simple. The OPLS-AA potential energy function incorporates bonding interactions as well as non-bonding interactions, like other potential energy functions. The bond-junction interaction consists of the Fourier torque potential, the harmonic bond length and bond angle potentials, and the bond-junction interaction, which consists of the LJ potential and Coulomb potential. The following are the force field expressions:
Fig 2. The functional form of the OPLS force field.
In addition to the BOSS and MCPRO programs, Alfa Chemistry implements OPLS force field analysis and simulation using a variety of well-known software packages, including TINKER, GROMACS, LAMMPS, PCMODEL, Abalone, Desmond, and NAMD.
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A remarkable feature of the OPLS parameters is that they are optimized to fit the experimental properties of the liquid, such as density and heat of vaporization, in addition to the gas-phase torsional profile.
- The carbon parameter in OPLS-UA implicitly includes hydrogen atoms next to carbon, which can be exploited to speed up simulations.
- OPLS-AA explicitly includes each atom. Parameters for more specific functional groups and molecular types are included in later publications (e.g., carbohydrates).
- The TIP4P or TIP3P water models are often used in OPLS simulations of aqueous solutions.
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- Abdel-Azeim S, et al. (2020). "Revisiting OPLS-AA Force Field for the Simulation of Anionic Surfactants in Concentrated Electrolyte Solutions." J. Chem. Theory Comput. 16(2): 1136-1145.