Recent content by sphericalCat

Hi, folks, Is the exponential (repulsive) term in Born-Mayer potentials supposed to be exp(-r) or exp(1/r)? - r is the interatomic distance; constants ignored I've seen both versions pop up in what appear to be reputable sources. The second one seems to be more popular, but, to me at...

Sorry, sloppy language on my part. We are talking about regions where charge can be found. What I basically am trying do is to add a repulsive component to a Madelung energy calculation, so I need something to represent ionic cores of finite size.

Another daft chemist question: I'm looking at two charges spread over two overlapping Gaussians. I want the energy of the interaction, so, I take qq'/r and integrate first over one Gaussian then over the other... except for it all goes up the spout, because the charges are overlapping, and...

Just, finally, finished reading your reply from beginning to end. Thank you very, very much. It has cleared most of the mess in my head. Still a bit confused abot what happens at the Gamma point, where there is no finite wavelength or fixed direction of propagation. Do you just define directions...

Thanks, once again, for the reply. Again, all makes sense, but... what i want to know is, basically, this: 1) Any given k-point can describe three normal modes, which, depending on symmetry, may or may not be degenerate. Is there a customary way of labelling these individually. My book (Hook...

Folks, A lot of you seem to be missing one rather cruicial detail. Astronomy, even at the most basic level, is a precise science. The oldest cave paintings are thought to be over 30,000 years old. That's about 24,000 years before the earliest signs of a coherent number system. Astronomy...

Ok, this all makes sense so far. By the way, as you suggested, I've gone back to the textbook, and things are, generally, beginning to make a bit more sense. Here's where I come unstuck: any given orientation vector can describe three orthogonal planewaves, right? Now, presumably, you can...

That much I know, but I was under the impression, that half the point of reciprocal space was to express the orientation vectors, describing periodic planes in real space, as discrete points in k-space. No?

Thanks for the pointer. I have looked at the textbooks before, but now, at least, I know which bits to concentrate on. One quick question about what you said: Am I wrong in thinking that, in the current context, the k-points correspond to real-space lattice vectors?

Hi folks, I'm having lots of trouble wrapping my head around this. For a start, how can you have a vibration along a [0 0 0] vector? I mean, where does it point?? And how can it have a finite momentum or frquency? (Does it?) Help would be greatly appreciated, but, please, speak slowly...