CASINO manual - Theory of Condensed Matter

8.10 TURBOMOLE
Website: www.turbomole.com
For the converter/interface, see the README file in ~/CASINO/utils/wfn converters/turbomole/.
This interface had stopped working until relatively recently, Martin Korth has supposedly revamped
this - but the current status is not clear. Feel free to ask Martin (mkorth at muenster.de).
8.11 Unsupported programs
If the program in question uses Gaussian, plane-wave, Slater or blip basis sets (or represents orbital
in a grid for atoms or dimers) then feel free to create your own converter to write the output of the
program in the appropriate [x]wfn.data format and send it to us (mdt26 at cam.ac.uk) for inclusion
in future releases. If you are the author/owner of the electronic structure package in question, then
you may like to add internal support so that the code can write out casino wave functions directly.
We can provide advice about this.
If your program uses some other basis set which requires a new casino orbital evaluator to be written,
then this could be a major project. Please ask.
8.12 Request for help
A final remark: support for plane-wave DFT programs is currently either ‘advanced’ (pwscf—in that
the program understands about blip functions and can do the necessary PW−→blip transformations
internally, and it can do DMC-MD calculations)—or ‘basic’ (castep, abinit, gp, mcexx). These
latter codes are only capable of writing out plane-wave pwfn.data files. If anyone would like to add
the blip stuff to e.g., castep or abinit then please volunteer: the routines can be essentially nicked
from pwscf, since we wrote them. Any volunteers coming forward to improve interfaces to other
codes would be very welcome.
9 Using CASINO with blip functions
Blip functions were devised by Mike Gillan and implemented in casino by Dario Alfè [23] (the original
implementation has since been significantly improved by many contributors).
Plane-wave DFT codes such as castep can be used to produce casino pwfn.data files with the
orbitals expanded in plane waves, but it is inefficient to use these directly in casino (though you can
if you want). Re-expanding the orbitals in a basis set of localized ‘blip functions’ on a grid makes
the code run faster and scale better with system size than it does with plane waves, though blips can
require a lot of memory and disk space.
The casino utility blip may be used to convert pwfn.data files generated by a plane-wave DFT
package into bwfn.data files. The pwscf software is capable of generating blip bwfn.data files (and
their binary equivalents) directly, and the use of this utility is unnecessary.
The quality of the blip expansion (i.e., the fineness of the blip grid) can be improved by increasing
the grid multiplicity parameter xmul (blip will ask you to supply this when it is run; in pwscf the
parameter is given as input in the pw2casino.dat file). A suitable default value is 1.0. Increasing
the grid multiplicity results in a greater number of blip coefficients and therefore larger memory
requirements, but the CPU time should be unchanged. For very accurate work, one may want to
experiment with xmul larger than 1.0. Note, however, that it might be more efficient to keep xmul
at 1.0 and increase the plane wave cutoff instead.
The blip utility will ask you whether you wish to carry out an overlap test. If you reply in the
affirmative then the converter will sample the wave function, the Laplacian and the gradient at a
large number of random points in the simulation cell and compute the overlap of the blip orbitals
with the original plane-wave orbitals:
α =
〈BW |P W 〉
√
〈BW |BW 〉 〈P W |P W 〉
(10)
The closer α is to 1, the better the blip representation. By increasing xmul, or by increasing the
plane-wave cutoff, one can make α as close to 1 as desired. The blip utility will as you for the number of
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