Help with an ideal gas canonical ensemble partition function integral

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SUMMARY

The discussion centers on the derivation of the volume term in the canonical ensemble partition function integral for an ideal gas. Participants confirm that the volume \( V \) arises from the integral \( \int \prod_{i=1}^N\left(d^3\vec{q}_i\right)=V^N \), where \( q_i \) represents the position coordinates of particles. Additionally, the conversation highlights the subsequent need to evaluate a 3N-dimensional Gaussian integral over the momenta of the particles, solidifying the understanding of the partition function's structure.

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AndreasC
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TL;DR
I'm reading Mehran Kardar's book on statistical mechanics, and it's great but super terse. I am trying very hard to understand a particular integral that is used over and over again for ideal gases, with no luck so far. Any help? I've posted a relevant picture below.
IMG_20201124_192841.jpg


Where does the volume even come from? Any help would be appreciated!
 
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AndreasC said:
Where does the volume even come from? Any help would be appreciated!

I'm not a physicist, but it looks just like ##\int \prod_{i=1}^N\left(d^3\vec{q}_i\right)=V^N## since the ##q_i## are presumably position coordinates.
 
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Infrared said:
I'm not a physicist, but it looks just like ##\int \prod_{i=1}^N\left(d^3\vec{q}_i\right)=V^N## since the ##q_i## are presumably position coordinates.
Oh, dammit, yeah, that where it comes from haha! Somehow I missed it. And then I guess the rest is just a 3N dimensional Gaussian integral over the momenta, right? Nice, that makes sense.
 

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