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Use the cluster expansion to write the total energy of a monatomic nonideal gas in terms of a sum of diagrams. Keeping only the first diagram, show that the energy is approximatelyU≈32NkT+N2V·2π∫0∞r2u(r)e-βu(r)drUse a computer to evaluate this integral numerically, as a function of T, for the Lennard-Jones potential. Plot the temperature-dependent part of the correction term, and explain the shape of the graph physically. Discuss the correction to the heat capacity at constant volume, and compute this correction numerically for argon at room temperature and atmospheric pressure.

Short Answer

Expert verified

Since, the energy isU=32NkT+2π·N2V·∫r2·u(r)e-β·u(r)dr. Hence, Proved.

The plot of the temperature-dependent part of the correction term is

Step by step solution

01

Given information

We have been given thatdU=-1Z·dZdβ=-ddβdZZ

02

Simplify

There are two terms in equation

U=Uid+Ue=-ddβlnZid-ddβlnZe

First term is equal to:

Uid=-ddβlnZid=32NkT

The second part is:

Ue=-ddβ12N2V∫u(r)d3r

Now, we will use the equation

Ue=-ddβ12N2V∫u(r)d3r=-ddβ12N2V4π·∫r2·u(r)dr

=-2π·N2V·∫r2·u(r)e-β·u(r)dr

The energy term is given by:

=32NkT+2π·N2V·∫r2·u(r)e-β·u(r)dr

The second virial coefficient is given by:

Ue=-ddβ12N2V∫u(r)d3r=-ddβ12N2V4π·∫r2·u(r)dr

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Most popular questions from this chapter

Consider an Ising model of just two elementary dipoles, whose mutual interaction energy is ±ϵ. Enumerate the states of this system and write down their Boltzmann factors. Calculate the partition function. Find the probabilities of finding the dipoles parallel and antiparallel, and plot these probabilities as a function of kT/ϵ. Also calculate and plot the average energy of the system. At what temperatures are you more likely to find both dipoles pointing up than to find one up and one down?

Consider a gas of "hard spheres," which do not interact at all unless their separation distance is less than r0, in which case their interaction energy is infinite. Sketch the Mayer f-function for this gas, and compute the second virial coefficient. Discuss the result briefly.

Show that the Lennard-Jones potential reaches its minimum value at r=r0, and that its value at this minimum is -u0. At what value of rdoes the potential equal zero?

For a two-dimensional Ising model on a square lattice, each dipole (except on the edges) has four "neighbors"-above, below, left, and right. (Diagonal neighbors are normally not included.) What is the total energy (in terms of ε) for the particular state of the 4×4square lattice shown in Figure 8.4?

Figure 8.4. One particular state of an Ising model on a 4×4square lattice (Problem 8.15).

Modify the ising program to compute the total magnetisation (that is, the sum of all the s values) for each iteration, and to tally how often each possible magnetisation value occurs during a run, plotting the results as a histogram. Run the program for a 5 x 5 lattice at a variety of temperatures, and discuss the results. Sketch a graph of the most likely magnetisation value as a function of temperature. If your computer is fast enough, repeat for a 10 x 10 lattice.

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