$npx -y skills add GPTomics/bioSkills --skill free-energy-calculationsPerforms alchemical free-energy calculations including relative binding free energy (RBFE / FEP+) and absolute binding free energy (ABFE) via OpenFE, FEP+, GROMACS, AMBER pmemd, and OpenMM with explicit lambda scheduling, soft-core potentials, MBAR/BAR analysis, cycle-closure val
| 1 | ## Version Compatibility |
| 2 | |
| 3 | Reference examples tested with: OpenFE 1.7+, OpenMM 8.1+, GROMACS 2024+, AMBER pmemd 22+, alchemlyb 2.1+, pymbar 4.0+, RDKit 2024.09+. |
| 4 | |
| 5 | Before using code patterns, verify installed versions match. If versions differ: |
| 6 | - Python: `pip show <package>` then `help(module.function)` to check signatures |
| 7 | - CLI: `openfe --version`; `gmx --version`; `pmemd.cuda --version` |
| 8 | |
| 9 | If code throws ImportError, AttributeError, or TypeError, introspect the installed |
| 10 | package and adapt the example to match the actual API rather than retrying. |
| 11 | |
| 12 | # Free Energy Calculations |
| 13 | |
| 14 | Predict binding free-energy differences (RBFE) or standard binding free energies (ABFE) using alchemical methods. FEP+ is a commercial workflow and OpenFE is an open-source framework. Accuracy and cost vary substantially with system, perturbation, force field, setup, sampling, and evaluation design; report the protocol and benchmark relevant to the intended decision. The Boltz-2 report includes benchmark-specific comparisons with FEP methods but does not replace prospective validation on the project chemistry. |
| 15 | |
| 16 | For docking input poses, see `chemoinformatics/virtual-screening`. For pose validation before FEP, see `chemoinformatics/pose-validation`. For ML alternatives, see `chemoinformatics/ml-docking-rescoring`. |
| 17 | |
| 18 | ## FEP Method Taxonomy |
| 19 | |
| 20 | | Method | Cost / pair | Accuracy | Use case | Fails when | |
| 21 | |--------|-------------|----------|----------|------------| |
| 22 | | FEP+ (Schrödinger) | System- and protocol-dependent GPU cost | Published commercial RBFE workflow | Commercial lead optimization | License and reproducibility constraints | |
| 23 | | OpenFE RBFE | System- and protocol-dependent GPU cost | Open-source RBFE with documented protocols | Open-source campaigns | Mapping/setup/sampling require review | |
| 24 | | OpenFE ABFE | Generally more setup and sampling than one RBFE edge | Standard binding free energy | No congeneric reference ligand required | Restraints and end-state corrections | |
| 25 | | GROMACS / AMBER RBFE | Implementation-dependent | Custom alchemical workflows | Expert-controlled setup | Manual validation burden | |
| 26 | | FEP-SPell-ABFE | Protocol/system-dependent | Automated ABFE workflow | Evaluate published and project benchmarks | Limited adoption | |
| 27 | | QligFEP v2.1 | Protocol/system-dependent | Q-based ligand FEP | Evaluate published and project benchmarks | Different approximations/tooling | |
| 28 | | MM/PBSA / MM/GBSA | Lower-cost endpoint analysis | Approximate endpoint score | Exploratory within-series comparison | Entropy, sampling, and model dependence | |
| 29 | | Boltz-2 affinity | seconds GPU | 0.66 Pearson on reported FEP benchmark subset | ML alternative; reported >=1000x lower cost | Novel chemotypes | |
| 30 | | ALEPB / EE-AMBER | Protocol/system-dependent | Specialized methods | Evaluate matched evidence | Limited tooling | |
| 31 | |
| 32 | **Decision:** For congeneric lead-optimization questions, evaluate a validated RBFE protocol and perturbation network. Use endpoint methods only for decisions supported by a project-specific benchmark. Candidate counts and escalation gates should follow compute budget, uncertainty, and prospective validation rather than a universal top-N rule. |
| 33 | |
| 34 | ## Decision Tree by Scenario |
| 35 | |
| 36 | | Scenario | Recommended workflow | |
| 37 | |----------|---------------------| |
| 38 | | Rank close analogs (R-group SAR) | RBFE via OpenFE (cycle: lig1↔lig2↔lig3) | |
| 39 | | Cross-scaffold ranking | ABFE per ligand; or coordinated RBFE with star network | |
| 40 | | Congeneric lead-optimization set | RBFE with a connected, redundancy-aware perturbation graph | |
| 41 | | Single ligand affinity | ABFE (no reference needed) | |
| 42 | | Lower-cost exploratory ranking | A project-validated endpoint or ML method, followed by orthogonal confirmation | |
| 43 | | Novel scaffold prospective | Treat ML affinity as triage; validate selected decisions prospectively | |
| 44 | | Selectivity (target vs off-target) | RBFE on both proteins; report delta-delta-G | |
| 45 | | Allosteric vs orthosteric | ABFE comparable; check pose stability with MD | |
| 46 | | Ions / metal centers | Specialized force field (ZAFF, MCPB.py); not standard FEP | |
| 47 | |
| 48 | ## Relative Binding Free Energy (RBFE) Setup |
| 49 | |
| 50 | **Goal:** Calculate delta-delta-G between two ligands (lig1 -> lig2) in pocket. |
| 51 | |
| 52 | **Approach:** Alchemical transformation lig1 -> lig2 in both bound state (pocket + ligand + water) and unbound state (ligand + water alone). Thermodynamic cycle: |
| 53 | |
| 54 | ``` |
| 55 | delta(delta-G_binding) = (delt |