Test of molecular mode coupling theory for general rigid molecules

Area of Science:

• Theoretical chemistry
• Condensed matter physics
• Statistical mechanics

Background:

• Mode coupling theory (MCT) is a theoretical framework used to describe the dynamics of supercooled liquids and glasses.
• Previous applications of MCT to molecular liquids often involved approximations, such as treating molecules as linear.

Purpose of the Study:

• To test the mode coupling theory for molecular liquids (MMCT) for molecules of arbitrary shape.
• To investigate the accuracy of MMCT in describing the dynamics of supercooled water.
• To compare theoretical predictions with molecular dynamics (MD) simulations.

Main Methods:

• Solving the full set of MMCT equations in the long-time limit for supercooled water, including all molecular degrees of freedom.
• Calculating nonergodicity parameters from the full MMCT equations truncated at l(co)=2.
• Comparing results with approximations (dipole and diagonalization) and MD simulations.

Main Results:

• The MMCT overestimates the glass-transition temperature (T(c)) for supercooled water, similar to findings for simple liquids.
• Nonergodicity parameters calculated from the full MMCT equations show discrepancies with approximations and MD simulations.
• The study highlights the impact of molecular shape on theoretical predictions.

Conclusions:

• The MMCT, when applied to arbitrary molecular shapes, overestimates the glass-transition temperature.
• Approximations in solving MMCT equations, such as reducing to prominent correlators, may be valid for rigid molecules.
• Further refinement of MMCT is needed for accurate predictions of supercooled liquid dynamics.