Recent content by Phileas.Fogg

Hello, I already finished my work @ nyxynyx : Do you want to know that, or do you try to help me? Because everything is finished already. I don't need any replies to this thread, but thanks. Mr. Fogg

Okay, thanks. I found an article, where the author says: J_{i,j} is a symmetric matrix containing the exchange parameters between spins at sites i and j. How does the spin vector operator look like, for Ions with spin e.g. 3/2 or 5/2 ? Regards, Phileas

Thanks peteratcam, I used the wrong expansion before, so I've the correct result now. How can J look like in this case? I think, it must be a 4x4 Matrix, right? Is the product of matrix J and the spin-spin-coupling matrix (I call it A) a tensor product, or just a normal matrix multiplication...

Hello, I'm studying the Heisenberg Model. Given the Hamiltonian H = - 2 \frac{J}{\hbar^2} \vec{S}_1 \vec{S}_2 with \begin{equation} \vec{S} = \frac{\hbar}{2} \; \left( \begin{array}{ccc} \sigma_x \\ \sigma_y \\ \sigma_z \end{array} \right) \end{equation} \sigma_{x,y,z} \quad...

Okay, I see. So from the Second Law, we get for the Gibbs Free Energy d(U+pV -TS) < 0 \Rightarrow dU +pdV - TdS < 0 . And to deal with the change in entropy, we take the Clausius (In)equation dS = \frac{\delta Q}{T} The system prefers the state with lower Gibbs Free Energy. So I have to...

Thanks, I understand now, one could explain it by taking a look at the p-T diagram. \lim_{T \to 0} \left( \frac{\partial p}{\partial T} \right)_V = 0 The coexistence curve starts at zero p and T and the fusion curve goes to infinity. So there must be a temperature in between, where a...

Can anybody answer my other questions?

Thanks DrDu, Since in equilibrium the Gibbs' Free Energy is a minimum, the system should prefer the lower chemical potential. So this should be correct, to gain energy from lower to higher potential. Mr.Fogg

Hello, right now, I am learning thermodynamics with Reichl: "A modern Course in Statistical Physics" In chapter 3.C page 100 "classification of phase transitions", the text says: "As we change the independent intensive variables (p, T, x_1,... ,x_l) of a system, we reach values of the...

:biggrin: :biggrin: :biggrin: Now I found my mistake. I didn't replace the dot with a comma in the file, I got. That's why there occurred these incredible angles :smile: Now I will revise my analysis and keep your help in mind. When a question occurs, I will ask you again. Thank You...

The new wave vector in our experiment is final minus initial wave-vector: \vec{q} = \vec{k}_f - \vec{k}_i and it's z-component is q_z = 2 k \sin(\alpha_i)

One measured peak is for example at 2 \Theta = 157523,511 °. In my calculation 1) Division by 2 gives \Theta = 78761,756 ° 2) Converting into radiants (for OpenOffice Calc) gives \Theta = 1374,652 3) now calculating (with OpenOffice Calc) \sin(\Theta) = -0,979 So I get a negative...

Thank You, where can I get the JCPDS file? When I convert the measured angle 2 \Theta into the z-component of the wave vector with q_{z,i} = \frac{4 \pi}{\lambda} \sin(\alpha_i) do I have to halve 2 \Theta ? Mr. Fogg

Hello, thanks! Do I also have to convert 2 \Theta into Radians when I use the Bragg's Law? In my calculation, I sometimes get a negative d , is that possible? How do I Index the peaks with Miller Indices? I don't know, how this equation helps me \frac{1}{d_{hkl}^2} = \frac{4}{3}...

Hello, I have X-Ray Diffraction Data: Intensity versus angle 2 \Theta and shall find out the lattice constant and even better the crystal structure. The Data is from a \Theta-\ThetaDiffractometer. \lambda = 1,54 \cdot 10^{-10}m I know that I have to find the peaks and can calculate d from...