Recent content by t!m

Indeed, I had in mind large-gap insulators. But perhaps even for gaps on the order of eVs, you can still use a relatively small bias? One other technicality is that many of these techniques (PES and presumably STM) are surface sensitive, and the band gap near the surface isn't necessarily the...

One can do inverse photoemission to probe the empty (conduction band) states, although the measurement is much harder than conventional (occupied) photoemission. Also if I'm not mistaken, tunneling spectroscopy requires a few additional assumptions to hold true, to be interpreted in terms of...

1. The location of high-symmetry points very much depends on the choice of the unit cell. A larger real-space unit cell (like a supercell) will have a different Brillouin zone, and therefore different high-symmetry points. In certain reduced units (i.e. in units of the real-space unit cell...

Storing a continuous space as a lattice of points is indeed the most common representation. In most all cases, this can be done in a controlled manner. Specifically, for a space of linear length ##L##, discretized using ##N## points on a lattice (stored in an array), there is a lattice spacing...

These are also different physical systems, due to the implied periodicity of these calculations. The first has a density of one Co atom per 3x3 cell of graphene, versus one Co atom per 4x4 cell of graphene - so the second implies a lower density of Co ad-atoms, and therefore a reduced Co-Co...

The property in question is the electron affinity, which is indeed positive in most materials (indicating that the energy of the N+1 electron system is less than that of the N electron system). For example, all atoms (except the noble gases) exhibit a positive electron affinity. Regarding your...

Energy-resolved photoelectron spectroscopy gives almost exactly the DOS. Angle-resolved PES (ARPES) gives the band structure (which can be projected onto the energy axis to give the DOS). Strictly speaking, this conventionally gives only the occupied states and one must do inverse PES (where...

For a 1D Ising model, the transfer matrix is ##2\times 2##. For a 2D Ising model on an ##N\times N## lattice, the transfer matrix is ##2^N\times 2^N##, and the thermodynamic limit requires infinitely large matrices, ##N \rightarrow \infty##! Nonetheless, this can be done and used to derive the...

Solar cells are not made out of metals but rather out of semiconductors, with a band gap around 1 eV to match the solar spectrum. Light from the sun hits the semiconductor and is absorbed, producing an electron-hole pair known as an exciton. Ultimately, the electron must be taken out one end...

This should help get you started, and should easily generalize to a two-dimensional base as you require: http://www.codingunit.com/c-tutorial-a-star-pyramid-and-string-triangle-using-for-loops You might have to think a bit more carefully about what the underlying crystal structure should be...

The OP may well have been asking if there are algorithms to generate "random" structures, which would then ultimately be studied in the ways Borek suggested. I don't think there is a generic answer to this question, and depends more on the application and structure of interest. For example, a...

Which part is unfamiliar to you? The general linear response formula involves the time correlation function of the observable and the applied field. In a Hall measurement, the current is measured in the direction orthogonal to the applied field, which is why vx and vy show up. Writing the...

As ZapperZ said, this is precisely what the electron-phonon coupling diagrams look like: https://www.google.com/search?tbm=isch&q=electron+phonon+diagram Feynman diagrams are indeed an appropriate way to describe this interaction (in a very rigorous way!), see e.g. Mahan's Many Particle Physics...

The problem with taking the product of the individual densities of states is that you are not enforcing that the transitions take place at a given value of the vector k. Remember that the density of states is only a function of energy, not k; it is only for the free electron (parabolic)...

We have to be a bit more careful in definitions here. From your figure, you can see that valence band dispersion is given by E_v(k) = -\hbar^2 k^2/2m_v and the conduction band is given by E_c(k) = E_g + \hbar^2 k^2/2m_c. From this you can work out the density of states for each band (there is...