Biochemical and Organic Simulation System
Monte Carlo statistical mechanics and molecular mechanics for organic and biological molecules in solution. Developed over forty years in the Jorgensen group at Yale University, BOSS is the computational core of the Foundation's simulation platform.
BOSS performs molecular mechanics (MM) and Monte Carlo (MC) statistical mechanics simulations on organic and biological molecules, with the goal of computing thermodynamic, structural, and energetic properties in solution. It combines the OPLS family of force fields with semi-empirical quantum mechanical methods to cover a wide range of chemical systems — from small organic molecules to protein active sites.
Monte Carlo Simulation
Statistical mechanics sampling in NPT, NVT, and μVT ensembles using Metropolis Monte Carlo. Handles periodic boundary conditions and standard cutoff schemes for efficient large-system treatment.
Energy Minimization
Full molecular mechanics energy minimization using conjugate gradient and steepest descent methods. Normal mode analysis for vibrational frequency computation and thermochemical corrections.
Free Energy Perturbation
Statistical perturbation theory for computing relative and absolute free energies of hydration, binding, and chemical equilibria. Thermodynamic integration as an alternative estimator.
Semi-empirical QM
AM1, PM3, and PDDG/PM3 Hamiltonians for electronic structure calculations. QM/MM hybrid calculations with OPLS-AA for the MM region, enabling accurate treatment of reactive centres.
Conformational Analysis
Systematic and Monte Carlo conformational searching for flexible molecules. Torsional scanning and geometry optimisation to map potential energy surfaces and identify low-energy conformers.
Solvation Studies
Explicit solvent simulations using TIP3P, TIP4P, and other water models. Radial distribution functions, solvation free energies, and solute-solvent interaction energies as primary outputs.
MM Energy Minimization
Full molecular mechanics minimization using the OPLS-AA, OPLS-UA, or AMBER force fields. Gradient minimization via conjugate gradient and limited-memory BFGS (L-BFGS). Supports constrained minimization, distance constraints, and dihedral restraints. Normal mode analysis available post-minimization for frequency computation and zero-point energy corrections.
Monte Carlo Statistical Mechanics
Metropolis Monte Carlo sampling in NPT (constant pressure-temperature), NVT (constant volume-temperature), and μVT (grand canonical) ensembles. Z-matrix internal coordinate moves for efficient conformational sampling of solute molecules. Preferential sampling of solute-solvent interactions. Standard periodic boundary conditions with minimum image convention and spherical or atom-based cutoffs.
OPLS Force Fields
Full implementation of OPLS-AA (all-atom) and OPLS-UA (united-atom) force fields. Covers organic molecules, proteins, nucleic acids, and lipids. Non-bonded interactions via Lennard-Jones 12-6 potential and Coulombic electrostatics. 1–4 interaction scaling at 0.5 for both LJ and electrostatics. Automatic atom typing for standard functional groups; custom parameter specification supported via input files.
Semi-empirical QM Methods: AM1, PM3, PDDG/PM3
Austin Model 1 (AM1), Parametric Method 3 (PM3), and the Pairwise Distance Directed Gaussian (PDDG/PM3) Hamiltonian. PDDG/PM3 provides improved heats of formation and thermochemical accuracy over standard PM3. Applicable to geometry optimization, single-point energy calculations, and QM/MM hybrid simulations. Supports open-shell (UHF) and excited-state calculations.
Free Energy Perturbation (FEP)
Statistical perturbation theory (Zwanzig equation) for computing free energy differences between chemical states. Supports double-wide sampling and multi-state FEP with overlap criteria. Thermodynamic integration (TI) as an alternative protocol. Applications include relative hydration free energies, conformational free energy differences, pKa prediction, and alchemical transformations between ligand analogues.
Solvent Models
Explicit water models: TIP3P, TIP4P, TIP4P-Ew, SPC/E. Explicit organic solvents: chloroform, DMSO, methanol, cyclohexane, and others parameterized against experimental liquid properties. Implicit solvent via GB/SA continuum model for rapid solvation free energy estimation. Gas-phase calculations supported for all methods.
What BOSS reads
Z-matrix (.z) files
Native BOSS internal coordinate format. Defines molecular geometry, connectivity, atom types, and partial charges. Required for all solute molecules.
Protein Data Bank (.pdb)
Standard PDB format for input protein and small-molecule structures. Automatic conversion to z-matrix available via the BOSS preprocessing utilities.
Tripos MOL2 (.mol2)
Small-molecule format with atom typing and partial charge information. Supported for ligand input with automatic z-matrix generation.
Structure Data File (.sdf / .mol)
MDL SDF format for small molecule libraries. Batch input supported for FEP series calculations across multiple ligand analogues.
Parameter files (.par)
Custom OPLS parameter files for novel functional groups or modified residues. Override standard library parameters for specific atom types.
What BOSS returns
Energy summary files
Total potential energies, component breakdowns (bonded, non-bonded, solute-solvent), ensemble averages, and standard deviations across the MC trajectory.
Simulation trajectories (.pdb / .xyz)
Coordinate snapshots at user-defined intervals. Viewable directly in the platform's 3D visualisation suite or exported for external analysis.
Free energy results
ΔG values with statistical uncertainties, overlap matrices, convergence plots, and per-window averages. CSV export for downstream analysis.
Radial distribution functions
Solute-solvent and solvent-solvent pair distribution functions, coordination numbers, and hydrogen bond statistics from completed simulations.
Full calculation log
Complete record of input parameters, system setup, convergence diagnostics, and all numerical results. Downloadable as plain text for archiving and methods sections.
Molecular Modeling of Organic and Biomolecular Systems Using BOSS and MCPRO
Journal of Computational Chemistry · 2005 · Vol. 26, pp. 1689–1700
Jorgensen, W. L.; Tirado-Rives, J. "Molecular Modeling of Organic and Biomolecular Systems Using BOSS and MCPRO." J. Comput. Chem. 2005, 26, 1689–1700.
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