Search for the surface states

This is option 7 of the main menu. It only works with CASTEP, see also Section 6.

You need a file psi2.SRF produced by lev1. The routine is interactive. First of all, a number of groups of states as well as states within each group should be specified. Then, the routine goes through states in each group one after another. Once the file psi2.SRF is read in for the current group, $[n_{1},n_{2}]$, the total charge contained in it is shown for your examination. Then, you have the following options:

• plot the sum of the $z$-densities taken over all states $n$ in the group $[n_{1},n_{2}]$; a plot of the density along the lattice vector $\mathbf{a}_{3}$ will be shown on the screen; the width of the plot corresponds to the length of the vector;
• plot every $z$-density for each state $n$ separately; this option works in the same way as the previous one; due to technical reasons, only 8 states are shown simultaneously on one picture; if you have more than 8 states in your current group, all of them will be shown by portions of 8, one after another; the last portion may contain less curves.

You can then start a new session. Data and Postscript files produced during one run have the following names: zdr.datN_M.K and zdr.datN_M.K.ps, where N is the group number, M is the session number and K is either the number of the plot (if every $z$-density is shown separately) or just 0 for the sum of $z$-densities.

Note that if the lattice vector $\mathbf{a}_{3}$ is perpendicular to the terraces of the slab, then these plots give you insight into how wavefunctions $\psi_{n\mathbf{k}}(\mathbf{r})$ for each band $n$ (or for a set of bands) are distributed along the width of the slab. If a wavefunction is concentrated mostly near edges of the slab, it corresponds to surface states; otherwise, it makes up one of the bulk states. Once you know exactly which states are surface states, then you can study the DOS of your slab paying special attention to the features in the DOS associated with these states.