Coupled Anharmonic Thermochemistry from Stratified Monte Carlo Integration

Area of Science:

• Computational Chemistry
• Chemical Thermodynamics
• Molecular Modeling

Background:

• Accurately calculating gas-phase thermodynamics requires handling molecular anharmonicity.
• Existing methods for anharmonicity can be computationally expensive or limited in scope.
• Developing black box, scalable methods for anharmonicity is crucial for molecular simulations.

Purpose of the Study:

• Introduce configuration integral Monte Carlo integration (CIMCI), a novel semiclassical method.
• Address limitations of current methods for fully coupled anharmonicity in gas-phase thermodynamics.
• Demonstrate CIMCI's applicability, scalability, and accuracy across various molecular systems.

Main Methods:

• Configuration integral Monte Carlo integration (CIMCI) employs stratified, simultaneous Monte Carlo integration.
• The method utilizes a modified MISER scheme for improved convergence rates.
• CIMCI is tested with primitive force fields (e.g., UFF) for efficiency.

Main Results:

• CIMCI shows superior accuracy in anharmonic entropy corrections compared to VPT2 and hindered rotor models for H2O and H2O2.
• The method demonstrates good agreement with 1D hindered rotor treatments for H2O2 and NH2OH at low temperatures.
• CIMCI achieves high accuracy even with less sophisticated force fields.

Conclusions:

• CIMCI offers a promising black box solution for gas-phase anharmonicity.
• The method exhibits favorable scaling properties for higher-dimensional systems.
• CIMCI provides a robust and accurate approach for thermodynamic calculations in computational chemistry.