CASINO manual - Theory of Condensed Matter

OPT MAXITER (Integer) Largest permitted number of nl2sol or global EMIN iterations (default:
10).
OPT METHOD (Text) There are currently four optimization methods implemented in casino:
(1) variance minimization (‘varmin’); (2) minimization of the mean absolute deviation of the
set of local energies from the median (‘madmin’); (3) energy minimization (‘emin’); (4) an
accelerated variance minimization technique for parameters that appear linearly in the Jastrow
factor (‘varmin linjas’). The first three methods are capable of optimizing the Jastrow factor,
orbitals, backflow functions, and determinant coefficients. The fourth method can only be used
to optimize linear parameters in the Jastrow factor. There are other keywords that affect the
behaviour of each of these methods. The default value of opt method is ‘varmin’.
OPT NOCTF CYCLES (Integer) Supplying a positive integer X for this keyword will cause all
cutoff parameters (in the Jastrow factor, backflow function and orbital functions) to be fixed for
the final X cycles of an optimization. Defaults to 0 for variance minimization, and to 50% of
total cycles for energy minimization.
OPT ORBITALS (Logical) Optimize parameters in the orbitals in wave-function optimization (relevant,
e.g., if use orbmods=T).
OPT STRICT (Logical) Setting opt strict=T will cause casino to stop a vmc opt or opt vmc run
if the VMC energies are incremented within a 99.7% confidence interval during two consecutive
cycles. Prevents wastage of CPU time in times of scarcity. Default value is F.
ORB NORM (Real) Allows user to change normalization of orbitals by multiplying all of them by
this constant. Of course this should have no effect on the energy, but it can be useful if the
Slater determinant starts going singular, as it might for some very low-density systems.
ORBBUF (Logical) Setting orbbuf=T turns on orbital buffering in DMC. This is an efficiency
device in which buffered copies of orbitals/gradients/Laplacians are kept for later reuse. This
has a significant memory cost. Orbital buffering should always be used unless you start running
out of memory; hence the ability to turn it off.
PAIR CORR (Logical) Set pair corr to T to accumulate the reciprocal-space pair-correlation function
in the expval.data file. Currently restricted to periodic systems. Note that you also need
to give the position and type of a fixed particle using the pcf rfix block (unless the density is
homogeneous). See Sec. 33.
PAIR CORR SPH (Logical) If pair corr sph is set to T then the spherically averaged real-space
pair-correlation function will be accumulated in the expval.data file (via a process of ‘binning’
the electron-electron separations). This currently works for periodic homogeneous systems and
finite isotropic systems such as electron-hole biexcitons. For periodic systems with atoms you
can use the pair corr keyword instead which gives you the full (non-spherically averaged) paircorrelation
function accumulated in reciprocal space. See Sec. 33.
PARTICLES (Block) Using the particles block the user can define quantum particles (other than
electrons, which can be introduced using neu and ned) to be used in the QMC calculation.
The format of each line is ‘〈i〉 〈charge/|e|〉 〈mass/m e 〉 〈spin/¯h〉 〈name〉’. A negative value of
the mass indicates that the following three lines give an anisotropic 3 × 3 mass tensor [currently
unused]. casino decides whether each particle type is a fermion or a boson (based on the spin),
and selects the appropriate way to combine the one-particle orbitals (symmetric combination
[not currently implemented] or antisymmetric Slater determinants). The particles defined here
can be assigned orbitals using the free particles block.
PCF RFIX (Block) This block contains two lines. The first line gives the type of particle to be
fixed during accumulation of the pair correlation function g(r, r ′ ); the second line gives the
coordinates of the position r at which to fix it (in a.u.). This applies to the reciprocal-space
PCF activated with the pair corr input keyword. It also applies in principle to the spherical
real space PCF activated with the pair corr sph input keyword, in the sense that the format
of expval.data allows it, but the accumulation of the spherical PCF with fixed particles has
not yet been implemented. See Sec. 33.
PERIODIC (Logical) T if and only if the system is periodic in either 1, 2 or 3 dimensions.
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