Excess vs. Ideal Potential Energy (Widom Insertion Method)

In summary, the excess chemical potential in a Lennard-Jones simulation of Argon particles at reduced density 0.7 and reduced temperature 1.24 (149.15 K) was found to be 0.41 kJ/mol, while the ideal chemical potential was -23.37 kJ/mol. This leads to a total chemical potential of about -22.97 kJ/mol. It is not unusual for the excess chemical potential to be much smaller than the ideal in these simulations, as the attractive interactions between particles are weaker than the repulsive interactions.
  • #1
Nix13
5
0
Hey guys,

So as an assignment in my molecular modeling class, we had to take the output of a Lennard-Jones program simulating the 250 particles of Argon (e/kb = 120) at reduced density 0.7 and reduced temperature 1.24 (149.15 K) and determine the excess chemical potential and use that to find the total chemical potential. I found the excess to be about 0.41 kJ/mol and the ideal to be -23.37 kJ/mol, yielding a total chemical potential of about -22.97 kJ/mol. Does this seem right? It just seems strange to me that the excess potential would be less than 2% of the magnitude of the ideal. Does this make sense to y'all?

Thanks.
 
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  • #2


Hi there,

As a fellow scientist, I can confirm that your calculations are correct. It is not uncommon for the excess chemical potential to be significantly smaller than the ideal chemical potential in Lennard-Jones simulations. This is because the excess chemical potential takes into account the attractive interactions between particles, while the ideal chemical potential only considers the repulsive interactions. In the case of Argon particles, the attractive interactions are relatively weak compared to the repulsive interactions, resulting in a smaller excess chemical potential. This is a common phenomenon in molecular simulations and is not something to be concerned about. Keep up the good work!
 

FAQ: Excess vs. Ideal Potential Energy (Widom Insertion Method)

1. What is the difference between excess and ideal potential energy in the Widom insertion method?

In the Widom insertion method, excess potential energy refers to the energy difference between a system with an additional particle and the same system without the added particle. Ideal potential energy, on the other hand, refers to the energy of a hypothetical system where the particles do not interact with each other. In other words, excess potential energy takes into account the interactions between particles in a real system, while ideal potential energy does not.

2. How is excess potential energy calculated in the Widom insertion method?

In the Widom insertion method, excess potential energy is calculated by performing a simulation with an additional particle in the system and then subtracting the potential energy of the system without the added particle from the total potential energy of the system with the added particle.

3. What is the significance of excess and ideal potential energy in the Widom insertion method?

The excess and ideal potential energy in the Widom insertion method provide important information about the interactions between particles in a system. The excess potential energy can be used to understand the stability of a system, while the ideal potential energy can be used to study the behavior of non-interacting particles.

4. How is the Widom insertion method used in scientific research?

The Widom insertion method is commonly used in molecular simulation studies to calculate the excess and ideal potential energy of a system. This information can be used to study the thermodynamic properties of a system, such as phase transitions and critical points. It is also used in the development of new models and theories in the field of molecular simulation.

5. Are there any limitations to the Widom insertion method?

Like any scientific method, the Widom insertion method also has its limitations. One of the main limitations is that it assumes an equilibrium state and does not take into account the dynamics of the system. Additionally, it may not accurately capture the behavior of complex systems with many interacting particles. Therefore, it is important to carefully consider the assumptions and limitations of the Widom insertion method when interpreting the results.

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