Calculator
Formula Used
Raw binding energy is calculated first.
ΔEraw = Ecomplex − (a × Ereceptor + b × Eligand)
Corrected enthalpy estimate includes additive chemistry corrections.
ΔHcorr = ΔEraw + BSSE + ZPE + Thermal + Solvation + Custom
Corrected free energy subtracts the entropy term.
ΔGcorr = ΔHcorr − TΔS
The dissociation constant estimate uses Kd = exp(ΔGcorr / RT). The free energy must be in joules per mole.
How to Use This Calculator
- Enter the total optimized energy for the molecular complex.
- Enter receptor and ligand energies from the same method.
- Set receptor and ligand coefficients for the model stoichiometry.
- Select one energy unit for every energy input field.
- Add BSSE, vibrational, thermal, solvation, or custom corrections.
- Enter the entropy term as TΔS in the selected unit.
- Press the submit button to show results above the form.
- Download CSV or PDF files for records and reports.
Example Data Table
| Entry | Value | Unit | Note |
|---|---|---|---|
| Complex energy | -150.4500 | Hartree | Optimized receptor-ligand complex |
| Receptor energy | -100.1200 | Hartree | Same method and basis |
| Ligand energy | -50.3000 | Hartree | Same charge state |
| BSSE correction | 0.0060 | Hartree | Counterpoise style correction |
| Entropy term | 0.0040 | Hartree | Entered as TΔS |
Binding Energy in Molecular Modeling
Binding energy describes how strongly two molecular parts associate. In a docking or quantum workflow, the complex energy is compared with separated fragment energies. A negative value usually suggests stable association. A positive value suggests weak or unfavorable association.
This calculator supports electronic energy and corrected free energy. It accepts complex, receptor, and ligand values. It also accepts stoichiometric coefficients. That helps when the complex contains more than one fragment. Optional terms cover BSSE, zero point correction, thermal correction, solvation correction, and entropy contribution.
Why Corrections Matter
Raw electronic energy is useful, but it is rarely the full story. Basis set superposition error can make binding look too favorable. Zero point energy accounts for molecular vibration at the ground state. Thermal correction adjusts the estimate toward the chosen temperature. Solvation correction helps compare gas phase and solution models. The entropy term often weakens binding because association reduces freedom.
For practical chemistry, compare values from the same method. Use the same geometry level, basis set, solvent model, and standard state. Do not mix energies from unrelated calculations. Small differences can come from convergence settings or restrained structures. Strong conclusions need consistent input.
Interpreting the Output
The tool reports raw binding energy, corrected enthalpy estimate, and corrected free energy estimate. It converts the final free energy into kJ/mol, kcal/mol, Hartree, and eV. It also estimates a dissociation constant using the relation between standard free energy and equilibrium. This estimate assumes ideal standard conditions. Treat it as a screening guide, not as final experimental proof.
A very negative free energy gives a small estimated Kd. That means stronger predicted association. A value near zero means marginal binding. A positive value gives a large Kd. That means dissociation is favored.
Use the export buttons to save results. The CSV file is suitable for spreadsheets. The PDF file is useful for reports. Keep the input table with your project notes. Record software settings too. Good records make molecular operating environment studies easier to review. They also reduce mistakes when many ligands are compared.
Repeat calculations after major geometry changes. Compare trends, not isolated numbers. When possible, validate top hits with experimental assays or higher level computations before ranking.
FAQs
What is molecular binding energy?
It is the energy difference between a complex and its separated parts. Negative values often suggest favorable association. The result depends strongly on the computational method and correction terms.
Can I use energies from docking output?
Yes, if all entries use the same unit and scoring convention. For strict thermodynamic work, use consistent quantum or molecular mechanics energies from comparable calculations.
What does BSSE correction mean?
BSSE means basis set superposition error. It can make a complex appear too stable. A counterpoise correction often reduces that artificial stabilization.
Why is entropy subtracted?
Free energy follows ΔG = ΔH − TΔS. When association reduces freedom, the entropy contribution may oppose binding. Enter TΔS using the selected energy unit.
Which unit should I choose?
Choose the unit used by your source data. Hartree is common for quantum chemistry. kJ/mol and kcal/mol are common for thermodynamic reporting.
What does a negative corrected free energy mean?
It suggests favorable binding under the assumptions entered. More negative values usually indicate stronger predicted association. Experimental validation is still important.
Is the estimated Kd exact?
No. It is an ideal estimate from corrected free energy and temperature. Standard state, solvent, sampling, and method choices can change real binding behavior.
Can I compare many ligands?
Yes. Use identical settings for every ligand. Export each result to CSV. Then compare corrected free energies and rankings in a spreadsheet.