CASINO manual - Theory of Condensed Matter

should pick out random.log files from different stages of a calculation (e.g., VMC configuration
generation / DMC equilibration / DMC statistics accumulation) and rename them appropriately.
Since 1.2011 (for more than 100 processors) the check on random seeds being equal on different
processors is only performed when RANPRINT is greater than zero.
REDIST GRP SIZE (Integer) In the branch-and-redistribute algorithm (which does redistribution
of configurations across nodes in DMC), we must decide which pairs of nodes are involved in configuration
transfers, and how many configurations are to be transferred in each operation. There
is an optimal algorithm for doing this (involving looking at individual configuration multiplicities
and the exact excess or deficit of configurations relative to a target on each node. If we consider
all the nodes then this algorithm scales linearly with the number of nodes, eventually becoming
so expensive that for a fixed number of configurations the code actually becomes slower if we
increase the number of nodes. We therefore parallelize the algorithm; to do this we form groups
of processors (‘redist groups’) of size redist grp size (plus some remainder). When calculating
the vector of instructions, only transfers within these groups are contemplated, and the cost for
working out what to send where no longer increases with the number of nodes (above a certain
size).
RELATIVISTIC (Logical) If relativistic is T, then relativistic corrections to the energy are calculated
using perturbation theory. Note that this can only be done for closed-shell systems at
present. See Sec. 32 for further details.
RNG RESTART SAFE (Logical) We would like, e.g., a 1000-move VMC run, and two 500-move
VMC runs linked together by a restart to give the same answer, in the sense that we end up with
the same vmc.hist file. Unfortunately they do not in general since the pseudorandom number
sequence is affected by the restart. This is because random numbers are generated something
like 63 at a time and stored in a buffer until needed (this buffer being refilled when necessary).
In the normal way of saving a point in the random number sequence, any unused numbers in
the buffer are discarded, which means the final answer will be different to the unrestarted case.
If the keyword rng restart safe is T (which is actually now the default) then the whole current
buffer is saved in the final config.out file as well as the current state of the random sequence
(necessarily fixed at the end of the current buffer). This allows multiple step runs to give the
same answer as single step runs, at the expense of slightly larger configuration files.
RUNTYPE (Text) This keyword specifies the type of QMC run to be carried out. It can take the
following values: ‘vmc’ (perform a single VMC simulation); ‘dmc equil’ (perform DMC equilibration);
‘dmc stats’ (perform DMC statistics accumulation); ‘dmc’ (perform DMC equilibration,
then statistics accumulation); ‘vmc dmc’ (perform VMC, then DMC equilibration, then DMC
statistics accumulation); ‘vmc dmc equil’ (perform VMC, then DMC equilibration); ‘opt’ (perform
a single wave-function optimization calculation); ‘vmc opt’ (perform opt cyles cycles of
VMC and optimization, alternately) ‘opt vmc’ (perform opt cycles cycles of optimization and
VMC, alternately); ‘gen mpc’ (generate an mpc.dat file enabling the use of the MPC interaction);
‘gen mdet casl’ (generate an mdet.casl file for use by the det compress utility); ‘plot’
(perform plot specified by block qmc plot). NOTE: in earlier versions of the code, we used
‘runtype : dmc’ with the now-redundant keyword ‘iaccumulate : T or F’ to indicate whether
stats accumulation was activated or not. This usage is now deprecated and, unless iaccumulate
is specifically defined in input, then ‘runtype : dmc’ is just a synonym for ‘runtype :
dmc dmc’.
SCELL MATRIX (Block) If the simulation-cell lattice vectors are {a i } and the primitive-cell lattice
vectors are {p j } then we may write a i = ∑ j S ijp j , where the S ij are integers. The 3 × 3 integer
matrix S is given in the scell matrix input block. This is a generalization of npcell (which
simply gives the diagonal elements of S in the special case that S is diagonal). Only one of
npcell and scell matrix should be present in the input file.
SHM SIZE NPROC (Integer) In Shm calculations on Blue Gene machines one needs to
know in advance the number of MB of shared memory required, so that one may set
the BG SHAREDMEMSIZE environment variable (which can be done by means of the
--user.shemsize argument to runqmc). casino will calculate this number and print it to
output at the end of the setup process (within the scope of testrun=T). However, the amount
of shared memory required depends on the number of cores (or the number of MPI processes
if running more or less than one process per core). If one ultimately wishes to run on, say,
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