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The Modified Poisson-Nernst-Planck (MPNP) model is a mathematical framework used to describe the transport of charged particles, such as ions, in a solution. It takes into account the effects of diffusion, electromigration, and electrostatic interactions on the movement of these particles.
The MPNP model incorporates additional terms to account for the effect of steric interactions between particles, which are not considered in the original Poisson-Nernst-Planck model. These steric interactions are important in systems with high particle concentrations or in confined spaces, such as biological cells.
The MPNP model assumes that the ions are in thermal equilibrium, the solution is dilute, and the particles are small enough that their movement is dominated by diffusion. Additionally, it assumes a continuum description of the solution and neglects the effects of hydrodynamic interactions between particles.
The MPNP model has been used to study a wide range of systems, including ion transport in biological systems, electrochemical reactions, and the movement of charged particles in microfluidic devices. It can also be applied to investigate phenomena such as electrophoresis, diffusion-limited reactions, and electrokinetic phenomena.
The MPNP model is typically solved numerically using computational methods, such as finite difference or finite element methods. These methods involve discretizing the equations and solving them iteratively to obtain a solution. Analytical solutions are also available for simplified versions of the model, such as the Debye-Hückel approximation.