Recent content by cgk

jaguar ride, there is chance that you should not study harder, but "lighter". Many people cannot cope with the level of stress you are putting up with for extended amounts of time. Especially once noticed that things go amiss. After a while, efficiency tends to start to drop rapidly. In fact, I...

My guess is that the author of that book confused "van der Waals interactions" (=*any* weak interaction, including residual forces between static multipoles) with "London dispersion force" (one of the many sources of weak interactions, between dynamic multipoles). CO2 certainly does have static...

I do not think that the question of "why zero resistivity?" is in any sense trivial or generally well explained in solid state textbooks. After searching myself and asking the same question (how do you get from BCS to zero resistivity?) to a number of high level active researchers in this domain...

JFS321, photons should not be considered as anything resembling classical particles. They are not small balls moving through space. The classical EM picture of waves is perfectly fine. You should keep it. The QM picture only comes in if your energy scales get small enough to notice individual...

The Bloch theorem is also not really that mysterious if you consider it's core meaning: If you have a bunch of symmetry operations which commute with the Hamiltonian, then the eigenstates of the Hamiltonian can be chosen in such a way that both the Hamiltonian and the symmetry generators are...

OP: I've spent some time at Cornell, and I really loved the university and the place. Living there is fantastic. But even so, I think moving for the reasons you mentioned (closer+slightly better rankings) seems like a very poor idea. The ranking of the university you go to for undergrad has...

Personally, I see little reason for reading up on popular science. Maybe it works for some, but most of it is somewhere between plain wrong (especially popular science about quantum mechanics) or oversimplified or hyped beyond recognition (especially thing about string theory, astrophysics and...

\vec f_1\cdot \vec f_2 = \Vert \vec f_1\Vert \cdot \Vert \vec f_2\Vert \cdot \cos(\alpha) (i.e., compute the scalar product, divide it by the vector norms, and you get the cosinus of the angle you are searching.)

First one (with the arrows) is much better (with the psi= on the left hand side, as Geofleur said in post #2). Everyone will understand the first one, it is effectively screaming "entanglement! That is me! looook at me, I'm entangled!", and it does not need any further definitions. Second one...

If you have the phi angle, you need the angle term. But the equations you wrote is how the angle term would look if \frac{\partial^2}{\partial\phi^2} applied to the wave function would give a value of "1" universally. I could understand if you set this term to zero (i.e., looking only for...

I missed the comment about the wave function being 0 on the inside of the cylindrical coordinate systems. So.. some extension. I probably should have expanded on how the boundary conditions come in: In the end, you just want to solve a linear algebra system---but only in the space you consider...

@OP: Regarding the boundary conditions: If you do not put in any additional information constraints, the (implicit) boundary conditions will be that the wave function is zero everywhere off the grid. That comes simply from the fact that there is no basis there to expand it, and thus your...

The determinant of of N vectors gives you the (signed) volume of the N-dimensional parallelepiped they span. Most of its uses come from either this property, or it's property as the simplest way of getting a totally anti-symmetrized product of stuff.

@OP: If you are just told to solve a certain problem, you are free to do it as you like. But if the task is explicitly to solve a given problem with a specific method, you have to use it to get full credit. There are reasons to force certain methods for solving a certain problem. In...

btw, I probably should have added this: A "first principles" calculation is not something you do with pen and paper. This is done with quantum chemistry software packages, which are complex scientific applications with often several 100k lines of code, and developed by many people over the range...