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fluidistic
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Homework Statement
Consider a system of N particles contained in a volume V. The Hamiltonian of the system is ##H=\sum{i=1}^N \frac{\vec p_i}{2m}+\sum _{i<j}u(|\vec r_i - \vec r_j|)## where p_i and r_i are the momentum and position of the i-th's molecule.
1)Show that the state equation of the system is ##\frac{Pv}{kT}=1+v\frac{\partial Z(v,T)}{\partial v }## where v=V/N and ##Z(v,T)=\frac{1}{N}\ln \left [ \frac{1}{V^N} \int d^3r_1... d^3 r _N \Pi _{i<j}(1+f_{ij}) \right ]##
Also ##f_{ij}=f(|\vec r_i -\vec r_j|)## with ##f(r)=e^{-\beta u(r)}-1##.
Homework Equations
Relation between P and Z: ##P=-\left ( \frac{\partial A}{\partial V} \right )_{\beta,N}##
Where ##A=-\frac{1}{\beta}Z_N(\beta, V)##
The Attempt at a Solution
I used the relevant equations to get ##A(\beta,V,N)=-\frac{1}{\beta} \ln [Z_N(\beta,V)]## so that ##P=\frac{1}{\beta}\frac{\partial}{\partial V} \{ \ln [Z_N(\beta,V)] \}##.
Hence ##\frac{PV}{kT}=V\frac{\partial}{\partial V} \{ \ln [Z_N(\beta,V)] \}##.
Dividing by N I reach ##\frac{Pv}{kT}=v\frac{\partial}{\partial V} \{ \ln [Z_N(\beta, V)] \}##
Now I believe that ##\frac{\partial}{\partial V} \{ \ln [Z_N(\beta,V)] \}=N\frac{\partial}{\partial v} \{ \ln [Z_N(v,\beta)] \}##.
Which yields ##\frac{Pv}{kT}=Nv \frac{\partial}{\partial v} \{ \ln Z_N (\beta ,v) \}=Nv\frac{1}{Z_N(v,\beta)}\cdot\frac{\partial}{\partial v}[Z_N(v,\beta)]##.
This differs from what I should have reached and I see no way to rewrite my expression into the desired one...
Any help on what's going on is appreciated.
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