Recent content by znbhckcs

That's very interesting. Thanks for your reply. The only thing that bothers me now is that when considering atoms with many electrons, in the central field approximation, the states are usually defined only by l1,l2... L,S mL and mS. Or at least, that's what I thought I knew... So is that not...

Obviously there are various way to add the third momentum, as is shown in your notation. But my question was, suppose we have a space defined by the quantum numbers l1,l2,l3 , m1,m2,m3 . We now add the momenta and get a space of l1,l2,l3,L,M, with M=-L,...L . But there are not enough states...

Hi I'm trying to figure out how to get the electric dipole selection rules for an atom with many electrons. In all textbooks that I've seen it's shown for Hydrogen, or in the central field approximation (which is, in some sense, equivalent to Hydrogen). Obviously the central field...

Hi It's easy to see that for addition of 2 angular momenta l1 and l2 , the space l1 m1 , l2 m2 is equivalent to the space of l1 l2 l m (where l is the total angular momentum). Counting the total number of states is usually a convenient way to make sure you got the addition right. But what...

I don't really see why you needed to go to the right hand side of the equation in the first place... You could have gotten that delta function right from the start. And all you get eventually is a conservation of momentum: k-k'+k''-k'''=0 . There is no further simplification... so I would...

Hi I've heard this term a few times and I couldn't find a definition in textbooks.. What is the definition of Particle-hole symmetry? I gather it's something like taking c -> c+ , but is there a definition of an symmetry operator that commutes with the hamiltonian or something? What does it...

But if the symmetry is visible because the crystal breaks only along these special plains, that would mean that the macroscopic crystal surface should be smooth to a very very high degree: almost to the level of a single atom. Is that true?

Yes. I mean the physical shape... for example look at this http://commons.wikimedia.org/wiki/File:Rock_salt_crystal.jpg" . And remember that NaCl is a cubic (fcc) lattice.

Ok, perhaps taking for granted was not a good way of putting it. I was trying to say this is a phenomenon to which I have never really given much thought. My question is what is the physical mechanism by which the microscopic structure is visible on a macroscopic scale? I am not talking...

I just noticed that it's often taken for granted that a macroscopic crystal has a similar geometric structure as in the atomic scale. What is the physical explanation for this (assuming it is true)?

Well, you are never really at zero temperature, and there are always other mechanisms to get a current going before reaching such a large voltage. So, of course my supposed experiment will not really work in a laboratory. But, theoretically, can one give meaning to the Fermi level in this...

Hi Strictly from the definition of the Fermi level as the highest energy occupied at zero temperature, it seems that in the presence of a band gap the Fermi level (Ef) could be placed fairly arbitrarily anywhere between the conduction (Ec) and valence (Ev) bands, since the density of states is...

Hi In Van Kampen's "Stochastic Processes in Physics" it says (page 79) that any given 2 non negative functions: p1(y,t), p11(y1,t1 | y2,t2) that satisfy: 1. The Chapman-Kolmogorov equation: p11(y3,t3 | t1,t1) = integrate(p11(y3,t3 |y2,t2) p11(y2,t2| y1,t1). 2. p1(y2,t2)= Integrate(p11(y2,t2...

The basic algorithm of degenerate perturbation theory is quite simple: 1.Write the perturbed Hamiltonian as a matrix in the degenerate subspace. 2.Diagonalize it. 3.The eigenstates are the 'correct' states to which the system will go as the perturbation ->0. But what to do if the first...