Starting with Version 1.25, the static code supports tight-binding calculations for collinear spin-polarized systems. Basically, the tight-binding parameter set is doubled, with one set of parameters for the up spin channel and another set for the down spin channel. A brief description of the method is found in Physica B 296, 125 (2001). (For the complete citation, see the Publications page.) Tight-binding parameters for most of the magnetic elements are available from the Tight-Binding parameters page.

In this example we will find the equation of state of ferromagnetic iron. Ferromagnets are particularly easy. The static code will do calculations for ferromagnets provided

• The mspin parameter in the P1 parameter file is set to 2,
• the code is recompiled, and
• a set of spin-polarized tight-binding parameters is available for the system.

In our case we'll use the spin-polarized parameters fe_ferro_par, available under iron on the Tight-Binding parameters page. Save these parameters in the working directory. Note that the first line of these parameters contains the string:

NM00000

The "M" parameter shows that this is a set of spin-polarized parameters. Note that the parameter list is twice as long as it is for, e.g. paramagnetic iron.

The rest of the operation is extremely similar to the calculation of the equation of state for a bcc material in Example I. In fact, we'll use the same space group (spcgrp.bcc) and k-point (bcc.08) as we did there. We can also use a similar SKIN file, or generate one using skingen. When everything is in place, our working directory will look like this:

$ ls -l
-rw-r--r-- 1  4604 Aug 30 16:27 SKIN
-r--r--r-- 1  2410 Jun  2  1995 bcc.08
-r--r--r-- 1 13217 Sep  1 17:02 fe_ferro_par
-r--r--r-- 1 10003 Jul 29 14:17 spcgrp.bcc

After compiling the code and running static, we find

$ ls -l
-rw-r--r--    1  1144 Aug 30 16:28 SKENG
-rw-r--r--    1  4604 Aug 30 16:27 SKIN
-rw-r--r--    1 33423 Aug 30 16:28 SKOUT
-r--r--r--    1  2410 Jun  2  1995 bcc.08
-r--r--r--    1 13217 Sep  1 17:02 fe_ferro_par
-rw-r--r--    1 31257 Aug 30 16:28 output
-r--r--r--    1 10003 Jul 29 14:17 spcgrp.bcc

Let's examine the SKENG file:

 4.500    45.562500    0.356042197    0.228434892    0.229156880  1.233912
 4.600    48.668000    0.316034846    0.164335413    0.164872466  1.369283
 4.700    51.911500    0.285898511    0.114703907    0.115281943  1.501013
 4.800    55.296000    0.260280591    0.076424707    0.077015904  1.638104
 4.900    58.824500    0.237816333    0.047718571    0.048344313  1.761880
 5.000    62.500000    0.218917315    0.026918725    0.027540422  1.879215
 5.100    66.325500    0.201760352    0.012792988    0.013433562  1.977186
 5.200    70.304000    0.186119122    0.004080878    0.004690274  2.055454
 5.300    74.438500    0.171962949   -0.000077659    0.000557350  2.113713
 5.400    78.732000    0.160793197   -0.000774238   -0.000140075  2.191955
 5.500    83.187500    0.151460298    0.001146919    0.001709833  2.260237
 5.600    87.808000    0.143739773    0.005279144    0.005820990  2.318224
 5.700    92.596500    0.138651781    0.011119144    0.011680794  2.380300

The first five columns are, as usual, a label (here the bcc lattice constant), the unit cell volume, the Fermi level, the total energy, and the pressure. The sixth column is the spin polarization of the system, in other words the excess of majority spin electrons over minority spin electrons. This is a measure of the magnetization of bcc Fe. Note, however, that we've left out any contribution to the magnetic moment from the orbital motion of the electrons.

For more details of the calculation, you can look at the SKOUT file.

Look at more examples

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Current URL: http://web.archive.org/web/20111231202250/http://cst-www.nrl.navy.mil/bind/static/example17/index.html