Dear user (please always sign the posts with name and affiliation)
Reading the manual and the papers (with a bit of testing) should help
answer your questions
'esm' :
Effective Screening Medium Method.
For polarized or charged slab calculation, embeds
the simulation cell within an effective semi-
infinite medium in the perpendicular direction
(along z). Embedding regions can be vacuum or
semi-infinite metal electrodes (use "esm_bc" to
choose boundary conditions). If between two
electrodes, an optional electric field
('esm_efield') may be applied. Method described in
M. Otani and O. Sugino, "First-principles calculations
of charged surfaces and interfaces: A plane-wave
nonrepeated slab approach", PRB 73, 115407 (2006).
NB:
- Two dimensional (xy plane) average charge density
and electrostatic potentials are printed out to
'prefix.esm1'.
- Requires cell with a_3 lattice vector along z,
normal to the xy plane, with the slab centered
around z=0.
- For bc2 with an electric field and bc3 boundary
conditions, the inversion symmetry along
z-direction
is automatically eliminated.
- In case of calculation='vc-relax', use
cell_dofree='2Dxy' or other parameters so that
c-vector along z-axis should not be moved.
See "esm_bc", "esm_efield", "esm_w", "esm_nfit".
+--------------------------------------------------------------------
+--------------------------------------------------------------------
Variable: esm_bc
Type: CHARACTER
See: assume_isolated
Default: 'pbc'
Description:
If "assume_isolated" = 'esm', determines the boundary
conditions used for either side of the slab.
Currently available choices:
'pbc' :
(default): regular periodic calculation (no ESM).
'bc1' :
Vacuum-slab-vacuum (open boundary conditions).
'bc2' :
Metal-slab-metal (dual electrode configuration).
See also "esm_efield".
'bc3' :
Vacuum-slab-metal
What does this mean "open boundary conditions", it is not clear!
It means that the asymptotic values of the potential along +z and -z
are not anymore constrained by periodic boundary conditions. The
behavior of the potential depends on the esm_bc value. using bc2
(metal-slab-vacuum) you should in principle (bc1 works very well in my
experience; I've never personally tested bc2) be able to change the
Fermi level within the slab to simulate source/drain electrodes in
contact with organic semiconductors.
HTH
Giuseppe
Quoting Ola Starkolis <[email protected]>:
What does this mean "open boundary conditions", it is not clear!
I would like to run metal/organic/vacuum and using
assume_isolated = "esm"
esm_bc = "bc1"
I suppose that the system is periodic in x and y directions and
non-periodic in z. Is it right?
Thank you so much for your help in advance.
GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <[email protected]>
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