CASINO manual - Theory of Condensed Matter

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currently work for the non-grid-based or outdated pseudopotential formats (2,3,4 and 5).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