Path A - Module 43: Energy Minimization#

Experimental structures and manually built models often contain “hot spots”: atoms that are too close or bonds that are stretched. If you try to run a simulation on these, the system will “explode” (numerical instability).

In this module, you will learn to perform Energy Minimization to relax your complex and prepare it for molecular dynamics.

import molsysmt as msm
from molsysmt import systems

# Load our solvated complex
fibril = msm.convert('pdb:2BEG', to_form='molsysmt.MolSys')
msm.build.add_missing_hydrogens(fibril)
peptide = msm.build.build_peptide('KLVFF')
msm.build.add_missing_hydrogens(peptide)
molsys = msm.merge([fibril, peptide])

# Check energy before minimization
energy_before = msm.molecular_mechanics.get_potential_energy(molsys)
print(f"Potential Energy before relaxation: {energy_before}")

1. The Minimization Process#

The function potential_energy_minimization() uses numerical optimization to move the atoms slightly until the forces acting on them are near zero.

# Perform energy minimization
# Note: This might take a few seconds depending on your hardware
msm.molecular_mechanics.potential_energy_minimization(molsys, tolerance='10.0 kJ/(nm*mol)')

print("Minimization completed.")

2. Verifying Success#

A successful minimization should result in a significantly lower (more negative) potential energy.

energy_after = msm.molecular_mechanics.get_potential_energy(molsys)
print(f"Potential Energy after relaxation: {energy_after}")

diff = energy_before - energy_after
print(f"Energy reduction: {diff}")

3. Structural Stability#

Let’s check if the system maintained its shape after minimization. A good minimization relaxes the system without unfolding the protein.

# Compare the RMSD between original and minimized (you would need a copy for this)
msm.view(molsys)

🏆 Path A Challenge: The Relaxer#

  1. Synthesize a very crowded system (e.g., peptide + many ions in a very small box).

  2. Check the starting energy (it should be extremely high).

  3. Minimize the system and record how many iterations or how much time it took.

  4. Verify that no bond lengths are physically impossible after the process.

Your complex is now physically stable. In Module 44, we will learn how to parametrize the system using AMBER TLeap Integration for professional force-field assignment.