= Degeneracy-pressure bulk modulus
{title2=$K=(5/3)P=(2/3)nE_F$}
For a nonrelativistic zero-temperature <free electron model> with fixed particle number, <electron degeneracy pressure> obeys $P\propto(N/V)^{5/3}$. Consequently its <bulk modulus> is $K=-V(\partial P/\partial V)_N=5P/3=2nE_F/3$. At <temperatures> small compared with the <electron Fermi temperature>, the leading <isothermal compressibility> is $1/K$. This electronic contribution alone omits ionic binding and interaction corrections in a real <metal>.
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