CASINO manual - Theory of Condensed Matter

CUSTOM SPAIR DEP (Block) This input block can be used to create new spin-pair groupings
for the Jastrow factor, etc. For example, if one were studying a paramagnetic fluid bilayer,
with spin-up and spin-down electrons in one plane (spins 1 and 2) and spin-up and spin-down
electrons on the other plane (spins 3 and 4) then one would want sets of u(r ij ) terms for sameplane,
same-spin pairs, same-plane, opposite-spin pairs and opposite-plane pairs. Here is an
example:
%block custom_spair_dep
no_spair_deps 1 # Number of custom spin dependences spair_dep -1 3 #
Label (-1,-2,-3,...) and number of spin groups 1-1,2-2,3-3,4-4 1-2,3-4
1-3,1-4,2-3,2-4
%endblock custom_spair_dep
To use this spin-pair dependence, the ‘spin-dependence’ flag in e.g. the u term of the Jastrow
factor in correlation.data would be set to ‘−1’. All spin-pairs must be included in a group.
See also custom ssingle dep.
CUSTOM SSINGLE DEP (Block) This input block can be used to create new spin-single groupings
for the Jastrow factor, etc. Here is an example:
%block custom_ssingle_dep
no_ssingle_deps 1 # Number of custom spin dependences ssingle_dep -1 2
# Label (-1,-2,-3,...) and number of spin groups 1,2 3,4
%endblock custom_ssingle_dep
To use this spin-single dependence, the ‘spin-dependence’ flag in e.g. the χ term of the Jastrow
factor in correlation.data would be set to ‘−1’. All spins must be included in a group. See
also custom spair dep.
CUSTOM STRIPLET DEP (Block) This input block can be used to create new spin-triplet
groupings for the Jastrow factor, etc. Since their is no automated generation of spin-triplets,
this block is necessary whenever using a Jastrow H term. Here is an example:
%block custom_striplet_dep
no_striplet_deps 1 striplet_dep -1 3
1=1=3,1=1=4,2=2=3,2=2=4,1=3=3,1=4=4,2=3=3,2=4=4
1=1=1,1=1=2,1=2=2,2=2=2,3=3=3,3=3=4,3=4=4,4=4=4 1=2-3,1=2-4,1-3=4,2-3=4
%endblock custom_striplet_dep
DBARRC (Integer) dbarrc is the number of updates between full recalculation of the cofactor
(‘DBAR’) matrices. Every time an electron move is accepted in VMC or DMC, the ‘DBAR’
matrices are updated using the efficient Sherman–Morrison formula (Eq. (26) of Ref. [15]), which
is numerically unstable. As a precaution, the DBAR matrices and determinant are recomputed
from scratch from the orbitals in the Slater matrix every dbarrc∗N updates. The default value
is 100,000. See Sec. 18.
DENSITY (Logical) If density is set to T then the charge density is accumulated and written to
the expval.data file. (This can only be done for periodic systems and finite single atoms at the
moment; the finite molecule case has not been implemented.) See Sec. 33.
DIPOLE MOMENT (Logical) If this flag is set to T then casino will accumulate the expectation
value of the electric dipole moment p. It will also evaluate the expectation value of |p| 2 . The
data (p x , p y , p z ) and |p| 2 are written to vmc.hist or dmc.hist like energy components, rather
than into expval.data, and their value and error bars are determined by reblocking. This can
only be done for finite systems.
Note that the casino reblock utility reports only the components and not the magnitude
of the dipole moment in order to allow the user to decide how to deal with the symmetry.
Suppose that symmetry dictates the dipole moment will point in the x direction. The y and z
components should be zero, but there will be some noise when they are evaluated in QMC. If
you work out |p| = √ |p x | 2 + |p y | 2 + |p z | 2 then you will get something larger than |p x
|, tending
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