CASINO manual - Theory of Condensed Matter
CASINO manual - Theory of Condensed Matter
CASINO manual - Theory of Condensed Matter
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The exporter does not currently work on multiple processors if k-point parallelism is chosen. abinit<br />
does not store the full wave function on each processor but rather splits the k points between the<br />
processors, so no one processor could write out the whole file. The sort <strong>of</strong> plane wave DFT calculations<br />
usually required to generate QMC trial wave functions execute very rapidly anyway and will generally<br />
not require a parallel machine. The outqmc routine currently bails out with an error if this combination<br />
<strong>of</strong> modes is selected.<br />
If there is any doubt about the output <strong>of</strong> this routine, the first place to look is the log file produced<br />
by abinit: if there are any warnings about incorrectly normalized orbitals or noninteger occupation<br />
numbers there is probably something set wrong in the input file.<br />
There exists a utility called abinit sc to convert abinit pseudopotentials, as long as they are in<br />
grid-based formats, i.e., pspcod=1 or pspcod=6, to casino x pp.data format. The utility does not<br />
currently work for the non-grid-based or outdated pseudopotential formats (2,3,4 and 5).<br />
8.2 ADF<br />
See www.scm.com.<br />
The converter adf2stowf.py was developed for version 2008.01 <strong>of</strong> the adf code. It takes the output<br />
<strong>of</strong> a molecular adf calculation and produces a casino trial wave function in a Slater-type basis. The<br />
cusp condition is implemented as a simple linear constraint, which is enforced by projection in the<br />
converter. The effect <strong>of</strong> this projection may be significant for small basis sets.<br />
In our experience, the ZORA/QZ4P basis set has been found to perform well.<br />
Importing frozen-core states is supported in principle. However, frozen-core states are not implemented<br />
in casino (no QMC algorithm for this is available at present). Therefore, adf frozen-core states are<br />
used as regular orbitals within casino.<br />
The adf converter and the Slater-type orbital implementation in casino have not yet been tested<br />
heavily, so expect bugs and limitations, which we will try to fix when reported.<br />
8.3 CASTEP<br />
The modern castep [7] is an entirely new Fortran 90 version <strong>of</strong> the venerable Cambridge planewave<br />
program which it is designed to replace. It is distributed by Accelrys as part <strong>of</strong> its Materials<br />
Studio package: see www.accelrys.com/products/mstudio/index.html. It is freely available to<br />
UK academics: see www.cse.clrc.ac.uk/cmg/NETWORKS/UKCP/castep.shtml. Mail Chris Pickard<br />
(c.pickard at ucl.ac.uk) to discuss castep and how to get hold <strong>of</strong> a copy.<br />
We assume that the reader is familiar with castep. (It takes about five minutes to learn how to<br />
perform basic castep calculations.) To generate a trial wave function using castep:<br />
1. Download the pseudopotentials that you need from http://vallico.net/casinoqmc/pplib/.<br />
You need to download the ‘tabulated’ file pp.data, which should be renamed as ‘x pp.data’,<br />
where x is the chemical symbol in lower-case letters, and the ‘casino awfn.data’ file for the<br />
ground state, which should be renamed as ‘x pp.awfn’. In your castep seedname.cell file<br />
allocate the pseudopotential to species ‘X’ using<br />
%block SPECIES_POT<br />
X x_pp.data<br />
%endblock SPECIES_POT<br />
Note that both x pp.data and x pp.awfn must be present.<br />
2. If you want to relax the geometry using these pseudopotentials, do so at this point. (However,<br />
it is generally best not to use casino’s HF pseudopotentials for DFT geometry optimization.)<br />
3. Specify your list <strong>of</strong> k points explicitly using the kpoints list block in seedname.cell (otherwise<br />
castep will apply symmetry operations to the k points in the grid). If you intend to use a<br />
complex wave function then you should supply the complete list <strong>of</strong> k points; otherwise you<br />
should only supply one out <strong>of</strong> each ±k pair. For example, the orbitals for a real wave function<br />
in a supercell consisting <strong>of</strong> 2 × 2 × 2 primitive cells could be constructed using the following<br />
k-point grid:<br />
101