CASINO manual - Theory of Condensed Matter
CASINO manual - Theory of Condensed Matter
CASINO manual - Theory of Condensed Matter
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The clearup twistav script can be used to clear up the output from a pwscf twist-averaging run.<br />
Default behaviour <strong>of</strong> twistav pwscf (on all machines):<br />
Note: in the following ntwist is 12, or the value <strong>of</strong> the optional argument --ntwist, while xwfn.data<br />
refers to whatever wave function file is specified in the pw2casino.dat file (either bwfn.data.b1<br />
[default], bwfn.data or pwfn.data).<br />
For a complete twist-averaging run, the following steps are performed in sequence:<br />
(A) pwscf generates ntwist xwfn.data.$ files, where $ is a sequence number from 1 to ntwist. Each<br />
succeeding run will have a different twist.<br />
(B) casino runs a full VMC or DMC run on each <strong>of</strong> the xwfn.data.<br />
On batch queue systems, twistav pwscf will by default do two batch script submissions, the first—<br />
handled by the runpwscf script—executing step (A), and the second—handled by the runqmc script—<br />
executing step (B).<br />
In principle, this wastes some unnecessary time (the time spent waiting for the QMC batch script to<br />
start) but this is unavoidable if twistav pwscf uses separate runpwscf and runqmc scripts to handle<br />
the DFT xwfn generation and QMC calculations. This may be changed in the future, if anyone can<br />
be arsed.<br />
Note that all calculations will be done on the number <strong>of</strong> cores requested on the command line (with<br />
the --nproc/-p flag) irrespective <strong>of</strong> whether they are DFT or QMC calculations. You may override<br />
this for the DFT calculations by using the --nproc dft flag to twistav pwscf.<br />
Modifications to default behaviour (on all machines)<br />
(1) twistav_pwscf --dft_only : execute only step (A), generating ntwist<br />
xwfn.data.$ files.<br />
(2) twistav_pwscf --qmc_only : execute only step (B).<br />
This requires that the ntwist xwfn.data.$ files already exist; if they don’t the script will whinge and<br />
die.<br />
(3) twistav_pwscf --startqmc=M : Start the chain <strong>of</strong> QMC runs with file xwfn.data.M .<br />
Modifications to default behaviour (batch machines only)<br />
On batch machines, there is an additional complication due to the walltime limits on particular queues<br />
which may require full twist-averaging runs to be split into sections. The following method may be<br />
used to do this.<br />
(4) twistav_pwscf --splitqmc=N : Split step B into N separate batch script<br />
submissions. If no value is supplied [--splitqmc] the run will be split<br />
into two.<br />
Example: ntwist=13, and twistav pwscf --splitqmc=4 will result in four step B batch submissions<br />
with 3, 3, 3, 4 twists.<br />
Note there is no facility for splitting step A into sections, i.e., all DFT wave function generation runs<br />
will always be run in a single batch script submission. This is because we assume the DFT runs are<br />
fast and you have adequate job time limits. If this is not the case then simply do multiple sets <strong>of</strong><br />
twistav pwscf runs.<br />
29 Finite-size correction to the kinetic energy<br />
29.1 Finite-size correction due to long-ranged correlations<br />
Consider a periodic system <strong>of</strong> N particles. Suppose there are N s species present, each with mass m α<br />
and charge q α , and let N α be the number <strong>of</strong> particles <strong>of</strong> type α. Let r iα be the position vector <strong>of</strong> the<br />
ith particle <strong>of</strong> type α. Let the simulation supercell have volume Ω.<br />
173