CASINO manual - Theory of Condensed Matter

of G vectors and discards all those before the first non-zero one (where zero is defined by some
threshold like 1.d-6). In the HF/DFT case this tends to give a large reduction in the size of the
vector to be evaluated. However, the random noise in the QMC density coefficients is likely to
exceed the zero threshold for all G, and the vector will likely be untruncated. It is important
therefore to use a value for expval cutoff which is not too large when using this facility, in
order that the total number of G vectors in the expansion is not too large.
QMC PLOT (Block) This utility allows you to plot the value of certain quantities along a line AB /
plane AB-AC / volume AB-AC-AD. The data will be plotted in a format suitable for xmgrace
in the file lineplot.dat or in a format suitable for gnuplot in 2Dplot.dat or 3Dplot.dat.
The block has the following format:
Line 1: what to plot (either ‘orb’, ‘orb gradx’, ‘orb grady’, ‘orb gradz’, ‘orb lap’, ‘wfn’, ‘nodes’,
‘energy’, ‘eipot’ or ‘expot’);
Line 2: dimensionality (1, 2 or 3);
Line 3: no. of points along each direction;
Lines 4–: (x, y, z) coordinates of point A; of point B; of point C (if required); of point D (if
required).
Three additional lines have to be added for orbital plots:
Line A1: number of orbitals (N orb );
Line A2: N orb integers identifying the orbitals to be plotted;
Line A3: N orb integers identifying the spins (1 or −1) for each of the orbitals.
For wave-function and local-energy plots, the coordinate defined by lines 4– refer to electron
1. The coordinates of all remaining electrons are taken from a configuration obtained by VMC
equilibration (without Jastrow factor). Alternatively the positions of several electrons may be
fixed. The following line(s) must be added:
Line B1: number of fixed electrons (≥ 0);
Line B2 and onwards: spin, number and (x, y, z) coordinates for each of the fixed electrons.
For electron–ion-potential, external-potential and node plots, no lines have to be added.
RANDOM SEED (String) This keyword determines which random seed to use for the RANLUX
random number generator. The default value of random seed is ‘default’, which uses the seed
314159265. If random seed is set to ‘timer’, the system timer will be used as the seed. If the
value of random seed is an integer, that integer will be used as the random seed. The seed is
printed to the output file so that calculations using random seed=‘timer’ can be reproduced
afterwards. Note that when restarting from a previous calculation the value of random seed
is ignored and the random number sequence will generally be continued from the saved state
of the random number generator stored in the config file. The user may in fact override this
behaviour in DMC restarts by setting random seed=‘timer’, in which case the generator will
be re-initialized from the system clock after the config file is read. This might be useful, for
example, if a prior test has revealed that the standard sequence will lead to a configuration
giving rise to a population explosion.
RANLUXLEVEL (Integer) To generate the parallel streams of pseudo-random numbers for its
stochastic algorithms, casino uses an implementation of the ranlux algorithm. This is an
advanced pseudo-random number generator based on the rcarry algorithm proposed in 1991 by
Marsaglia and Zaman. rcarry used a subtract-and-borrow algorithm with a period on the order
of 10 171 but still had detectable correlations between numbers. Martin Luescher proposed the
ranlux algorithm in 1993; ranlux generates pseudo-random numbers using rcarry but throws
away numbers to destroy correlations. ranlux trades execution speed for quality through the
choice of a ‘luxury level’ given in casino by the ranluxevel input keyword. By choosing a
larger luxury setting one gets better random numbers slower. By the tests available at the time
it was proposed, ranlux at its higher settings appears to give a significant advance in quality
over previous generators. The luxury setting must be in the range 0–4. Level 0: equivalent to
the original rcarry of Marsaglia and Zaman, very long period, but fails many tests. Level 1:
considerable improvement in quality over level 0, now passes the gap test, but still fails spectral
test. Level 2: passes all known tests, but theoretically still defective. Level 3 [DEFAULT]: any
theoretically possible correlations have very small chance of being observed. Level 4: highest
possible luxury, all 24 bits chaotic.
RANPRINT (Integer) Setting this keyword to a value greater than zero will cause the first ranprint
numbers generated by the casino random number generator to be printed to a file random.log.
On parallel machines the numbers generated on all processors are printed. The run script
51