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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 | This example shows how to use the Effective Screening Medium Method (ESM)
to calculate the total energy, charge density, force, and potential of a
polarized or charged medium.
ESM screens the electronic charge of a polarized/charged medium along one
perpendicular direction by introducing a classical charge model and a local
relative permittivity into the first-principles calculation framework. This
permits calculations using open boundary conditions (OBC). The method is
described in detail in M. Otani and O. Sugino, "First-principles calculations
of charged surfaces and interfaces: A plane-wave nonrepeated slab approach,"
PRB 73, 115407 (2006).
In addition to 'pbc' (ordinary periodic boundary conditions with ESM
disabled), the code allows three different sets of boundary conditions
perpendicular to the polarized medium:
1) 'bc1' : Immerse the medium between two semi-infinite vacuum regions;
2) 'bc2' : Immerse the medium between two semi-infinite metallic electrodes,
with optional fixed field applied between them;
3) 'bc3' : Immerse the medium between one semi-infinite vacuum region and one
semi-infinite metallic electrode.
The example calculation proceeds as follows:
esm_bc = 'bc1':
1) make a self-consistent calculation for H2O with esm_bc = 'pbc' (ESM off)
(input=H2O.noesm.in, output=H2O.noesm.out). Using 'pbc' causes the
code to print out the density and potential (hartree + local) along z, even
though ESM is disabled. Note that the molecule has a z-oriented dipole.
2) make a self-consistent calculation for H2O with esm_bc = 'bc1'
(input=H2O.bc1.in, output=H2O.bc1.out). This simulates the water molecule
in an infinite vacuum along the z-direction, preventing dipole-dipole
interaction between periodic images.
esm_bc = 'bc2':
3) make a self-consistent calculation for Al(111) with esm_bc = 'bc2',
without an applied field (input=Al111.bc2.in, output=Al111.bc2.out).
This simulates the slab sandwiched between two uncharged semi-infinite
metal electrodes.
4) make a self-consistent calculation for Al(111) with esm_bc = 'bc2',
this time with an applied field (input=Al111.bc2_efield.in,
output=Al111.bc2_efield.out). The slab polarizes in response.
esm_bc = 'bc3':
5) make a self-consistent calculation for Al(111) with esm_bc = 'bc3' to
simulate a semi-infinite system in contact with vacuum
(input=Al111.bc3.in, output=Al111.bc3.out).
6) make a self-consistent calculation for Al(111) with esm_bc = 'bc3' to
simulate a semi-infinite system in contact with vacuum with a weakly
negative (-0.005e) overall charge (input=Al111.bc3_m005.in,
output=Al111.bc3_m005.out). Note that the charge migrates to the surface/
vacuum interface.
7) Repeat #6 but with a weakly positive (+0.005e) overall charge
(input=Al111.bc3_p005.in, output=Al111.bc3_p005.out).
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