How To Correct Erroneous Symmetry-Breaking in Coarse-Grained Constant-pH Simulations

Area of Science:

• Computational chemistry
• Soft matter physics
• Biophysics

Background:

• The constant-pH Monte Carlo method is widely used for simulating acid-base equilibria in soft matter.
• This method encounters systematic errors when explicit ions are included, causing symmetry breaking in simulations.
• These errors affect simulations of systems like weak polyelectrolytes and proteins.

Purpose of the Study:

• To address and correct systematic errors in constant-pH Monte Carlo simulations with explicit ions.
• To develop methods for correcting the pH-scale artifact in these simulations.
• To provide guidelines for accurate simulations of charge-regulating soft matter.

Main Methods:

• Developed two analytical methods for a posteriori correction of the pH-scale.
• Employed a numerical method using Widom insertion for correction.
• Investigated various sample systems to validate the correction methods.

Main Results:

• Demonstrated that a simple pH-scale shift can correct systematic errors.
• Assessed the validity range of analytical correction methods through numerical simulations.
• Showed that the Widom insertion method consistently yields accurate results, even when analytical methods fail.

Conclusions:

• The proposed pH-scale shift effectively corrects artifacts in constant-pH simulations.
• The Widom insertion method offers a robust approach for error correction.
• Practical guidelines are provided for accurate simulations, especially for complex systems like polyampholytes and proteins.