Re: How to calculate entropy of particles?

On Feb 15, 6:12 am, Rick Giuly <rgiuly.gr...@xxxxxxxxx> wrote:
On Feb 14, 11:40 pm, Eric Gisse <jowr...@xxxxxxxxx> wrote:



On Feb 14, 9:22 pm, Rick Giuly <rgiuly.gr...@xxxxxxxxx> wrote:

Hello all,

I'm working on a molecular dynamics simulation based on Lennard-Jones
potential. Each particle has a position, a mass, and a velocity.

I know that temperature is the average kinetic energy of all the
particles, so temperature is no problem to calculate.

But, how would you calculate the entropy of the particles?

S = k ln(number of states)
dS = dQ / T

Any help is appreciated.

-Rick Giuly
If replying by email please use: rgiuly at ucsd dot edu

reference:http://en.wikipedia.org/wiki/Lennard-Jones_potential

The problem I have with S = k ln(number of states) is that it seems
like the number of states is nearly infinite, since there are multiple
particles and each can be at any location in space.

Do they obey a distribution? If so you can probably use a partition
function to obtain the entropy.


dS = dQ / T
This formula tells me something about how the entropy would change
when heat is added but I want to calculate the entropy as a function
of the position and velocity of all the particles at an instant in
time.

So I'm still not sure how to calculate the entropy (as a function of
the position and velocity of all the particles at an instant in time).

-Rick

.

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