CASINO manual - Theory of Condensed Matter

FORCES INFO (Integer) Controls the amount of information calculated/displayed during force
calculations:
‘2’: display no additional information; the Hellmann–Feynman force is evaluated with the d-
channel of the pseudopotential chosen to be local and the s-d and p-d channels nonlocal (default);
‘5’: calculate and display two additional Hellmann–Feynman force estimators, where the s- and
p-channels of the pseudopotential components are chosen to be local.
FREE PARTICLES (Block) This block sets the parameters that define the behaviour of the orbitals
which are not atom-related in a system. The geometry of the system can be given using ‘r s
〈r s 〉’, ‘dimensionality 〈d〉’ and ‘cell geometry’ (followed by d lines with d reals corresponding
to the unscaled cell vectors). For 2D or 1D systems one can also specify that the electrons
are confined to different layers (wires in 1D) using ‘heg nlayers 〈no. layers〉’ and ‘heg zlayer
〈layer〉 〈z〉’, with species being assigned to layers using ‘heg layer 〈spin〉 〈layer〉’. In 1D, one
can also specify the y-coordinate of a wire using ‘heg ylayer 〈layer〉 〈y〉’. These parameters
are only required if atom basis type=‘none’ (which it is by default) in the input file). The
number and type of the orbitals can be given using lines with the syntax ‘particle 〈i〉 det 〈det〉
: 〈n〉 orbitals 〈orb〉 [orb-options]’, where 〈det〉 is the term in the multideterminant expansion,
〈i〉 must be 1, 2 or a number given in the particles block (1 and 2 are up- and down-spin
electrons), 〈n〉 is the number of free particles/orbitals belonging to the 〈det〉th determinant
and ‘〈orb〉 [orb-options]’ is one of the following: ‘free’, ‘crystal sublattice 〈s〉’, ‘pairing 〈j〉’,
‘sdw’ or ‘expot 〉set〈’, 〈j〉 being the particle type with which 〈i〉 is paired and 〉set〈 being an
orbital set in expot.data. If the orbitals have optimizable parameters, these must be provided
in correlation.data. Wigner-crystal geometry is specified using the keywords ‘crystal type
〈type〉 〈n〉 sublattice[s] [repeat 〈r〉]’ (type = ‘cubic’, ‘fcc’, ‘bcc’, ‘rectangular’, ‘hexagonal’ or
‘triangular’, which must match ‘dimensionality’ and ‘cell geometry’, or ‘manual’), and ‘sublattice
〈s〉 [antiferro[magnetic]] offset 〈x y z〉’ for predefined lattices, and ‘sublattice 〈s〉 manual 〈n〉
site[s]’ followed by 〈n〉 lines of the form 〈x y z〉 defining the sites for manual lattices. If a
complex wave function is used, i.e., complex wf is set to T, then an offset to the grid of k
vectors for fluid phases may be specified using ‘k offset 〈k x 〉 〈k y 〉 〈k z 〉’, where k x , k y and k z are
the Cartesian components of the offset. The offset is translated into the first Brillouin zone of the
simulation cell. Using a nonzero offset corresponds to using twisted boundary conditions. It’s
not quite as difficult to use this input block as it may appear from the above: see the examples
in ~/CASINO/examples/electron phases and ~/CASINO/examples/electron hole phases.
FUTURE WALKING (Logical) If this flag is set to T then future walking will be used to evaluate
pure estimators in DMC. See Sec. 35.
GAUTOL (Real) Tolerance for Gaussian orbital evaluation.
neglected if its value is less than 10 −gautol .
The contribution of a Gaussian is
GROWTH ESTIMATOR (Logical) Turn on calculation of the growth estimator of the total energy
in DMC calculations. A statistically significant difference between the mixed estimator and the
growth estimator for the energy normally implies the presence of time-step bias. Other than
that, the growth estimator is not generally useful, because the statistical error in the growth
estimator is substantially greater than the error in the mixed estimator. See Sec. 13.8 for more
information.
HAVE AE (Logical) If have ae is F, casino expects to find pseudopotentials for all nuclei in the
system. The default value is guessed from the basis type (blip and plane-wave orbitals: F;
numerical and slater-type orbitals: T; Gaussian orbitals: depends on whether pseudo-ions with
Z > 200 are present). Only in exceptional cases will it be necessary to set have ae explicitly.
If all-electron ions and pseudo-ions are present, both have ae and allow ae ppots need to be
set to T.
IBRAN (Logical) If set to T then weighting and branching is allowed in DMC. Setting ibran=F
may be used to check the DMC algorithm, as it then reduces to a VMC algorithm in which the
DMC drift-diffusion Green’s function is the transition probability density.
INITIAL CONFIG (Block) Use this keyword if you want to specify the initial VMC configuration
to use instead of the random one generated by the points routine. It is possible to specify the
positions of only some of the particles. The format of each line in this block is:
σ i x y z
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