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Thermodynamics at low temperature

Finite temperature thermal corrections can be obtained by starting with the expansion derived earlier: Note that

eqnarray411

The term proportional to tex2html_wrap_inline913 is a small thermal correction to the T=0 limit. As such, it is small and we can replace the tex2html_wrap_inline855 appearing there with tex2html_wrap_inline919 to the same order in T:

displaymath429

Solving this, now, for tex2html_wrap_inline855 (which is equivalent to solving for tex2html_wrap_inline797 ) gives

eqnarray436

where the second line is obtained by expanding tex2html_wrap_inline927 about x=0.

In order to obtain the thermal corrections, one must expand the average occupation number formula about the tex2html_wrap_inline919 value using the expansion obtained above for tex2html_wrap_inline855 and the do the integrals. The result is simply

displaymath446

The thermal correction is necessary in order to obtain the heat capacity at constant volume, which is given by

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Using the above expression for the energy, one finds

displaymath454

From the thermally-corrected expression for the energy, the pressure can be obtained immediately:

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Mark Tuckerman
Sat Jan 4 22:04:30 EST 2003