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Thermodynamically self-consistent theories of fluids interacting through short-range forces
C Caccamo1, G Pellicane, D Costa
1Istituto Nazionale per la Fisica della Materia (INFM) and Dipartimento di Fisica, Università di Messina, Contrada Papardo, Salita Sperone 31, 98166 Messina, Italy. caccamo@vulcano.unime.it
Summary
This study compares four theories for hard-core Yukawa fluids, finding SCOZA and HRT best predict phase diagrams. While all theories show some limitations at low temperatures and high densities, SCOZA remains predictive for thermodynamic properties across various screening lengths.
Area of Science:
- Statistical Mechanics
- Physical Chemistry
- Soft Matter Physics
Background:
- The hard-core Yukawa fluid (HCYF) model is crucial for understanding complex fluids, including colloidal suspensions and protein solutions.
- Accurate theoretical models are needed to predict the thermodynamic and structural properties, as well as phase behavior, of such systems.
Purpose of the Study:
- To evaluate and compare the performance of four theoretical approximations: self-consistent Ornstein-Zernike approximation (SCOZA), generalized mean spherical approximation (GMSA), modified hypernetted chain (MHNC), and hierarchical reference theory (HRT).
- To assess their accuracy in predicting thermodynamic properties, structural characteristics, and the phase diagram of the HCYF across a range of screening lengths (lambda).
Main Methods:
- Application of SCOZA, GMSA, MHNC, and HRT to the HCYF model.
- Investigation of systems with varying Yukawa-tail screening lengths (lambda) from 1.8 to 9.
- Comparison of theoretical predictions with existing computer simulation data.
Main Results:
- At low screening lengths (lambda), all theories provide reasonably accurate predictions for thermodynamic and structural properties.
- SCOZA and HRT quantitatively predict the binodal line and critical parameters of the phase diagram.
- Discrepancies emerge at lambda=4, with MHNC accurately predicting energy and radial distribution function contact values, while SCOZA excels in predicting the equation of state up to the highest lambda values. GMSA and MHNC show inaccuracies in liquid coexisting densities, while SCOZA and HRT fall in between. SCOZA remains predictive at higher lambda values.
Conclusions:
- SCOZA and HRT demonstrate superior performance in predicting the phase diagram of HCYF, particularly at higher screening lengths.
- While all theories exhibit some limitations at low temperatures and high densities, SCOZA proves to be a robust model for thermodynamic properties.
- Further assessment of freezing predictions is necessary, though GMSA shows qualitative agreement with simulations for solid-vapor coexistence at high lambda.