CASINO manual - Theory of Condensed Matter

9. Clearly, the total number of possible forms of external potential is infinite, and the associated
geometries can be arbitrarily complex. It is therefore envisaged that new representations and,
if necessary, new ways of describing the geometry will be added to the expot.data file on a
case-by-case basis. At some stage, the ability to do full 2D and 3D Fourier expansions of the
external potential will be added.
10. The orbital bands will be filled in order, e.g., the second band will be started once the first one is
full. This is in contrast with an energy-based filling method which could also be implemented (on
request). All of the orbitals in a band have the z dependency given by the Fourier series, while
a different xy plane-wave will multiply each of them. Be sure to have odd occupation numbers
to keep translational symmetry—casino will stop otherwise—and to occupy your bands with
the right numbers to ensure isotropy as well, if required—casino will perform no checks in this
sense.
11. Fourier-expanded orbitals are pretty inefficient if what you want to represent is a set of orbitals
localized in the z direction. Numerical orbitals would be a neat alternative, and are easy to
implement, but as none of us is interested in this so far, this is unavailable. Contact us if you
would like to use such a thing.
12. Used with care, the plane-wave terms p and q in the Jastrow factor, together with the u term, can
often provide variational freedom that reflects the geometry of the external potential in periodic
systems. If you believe that your choice of external potential necessitates the development of
new types of term in the Jastrow factor then please discuss with the developers.
13. Note that the external potential is only applied to the quantum particles that are simulated;
constant potential energy contributions arising from, e.g., the interaction of an external electric
field with the fixed nuclei are not calculated by casino and must be added by hand.
14. Magnetic fields are also specified in the expot.data file. See Sec. 37.
7.10 Raw QMC data files: vmc.hist and dmc.hist
The raw VMC and DMC energy data are stored in files called vmc.hist and dmc.hist, respectively.
Although the files have different names, they have the same format. The .hist files contain the local
energy and its components as calculated during the QMC simulation; by averaging these, one obtains
estimates of the total energy, etc. Note that the raw data in the .hist files are the averages of the
local energies across the processors of a parallel machine. Furthermore, the VMC local energies are
averaged over vmc ave period evaluations before being written out, while the DMC local energies are
averaged over the current population of configurations. One cannot, therefore, calculate the variance
of the energy by computing the variance of the total-energy data in vmc.hist and dmc.hist. The
energy data should be analysed using the reblock utility (or quickblock if the file is very large).
The data in vmc.hist and dmc.hist can be extracted for plotting using the plot hist utility.
An example of a vmc.hist file is given below.
# Title
# My CASINO vmc.hist file.
# File version number
# 1
# QMC method (VMC, DMC, PIMC, AFMC or RMC)
# VMC
# Electron-electron interaction type (interaction keyword)
# ewald
# Constant (ion-ion) energy
# 2.34
# Number of electrons (and other particles) in simulation
# 48
# Number of atoms per primitive cell
# 12
# Number of primitive cells
# 1
# Basis type (from atom_basis_type keyword - formerly btype)
# gaussian
# Periodic (0=NO; 1=YES)
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