Linear expansion DeltaSCF
Electronic excitations of NO on Ni(001)
ATTENTION: These calculations are done using standard on-the-fly pseudopotentials from CASTEP-6.0.1
For this example we calculate a charge neutral HOMO->LUMO excitation and a charge transfer excitation between a nickel substrate and a NO molecule
In the following, the required input files are:
no-on-ni001.param, no-on-ni001.cell, gasphase.cell, gasphase.param, gasphase.check
no-on-ni001.param
#reuse: default
calculate_deltascf : true
deltascf_method : linear expansion
deltascf_checkpoint : gasphase.check
#band occ spin
%block deltascf_constraints
5 0.0000 1
6 1.0000 2
%endblock deltascf_constraints
task: SinglePoint
spin_polarized : True
cut_off_energy : 400.0
elec_energy_tol : 1e-07
fix_occupancy : False
iprint : 1
max_scf_cycles : 200
metals_method : dm
mixing_scheme : Pulay
mix_history_length : 7
nextra_bands : 50
num_dump_cycles : 0
opt_strategy_bias : 3
smearing_scheme : Gaussian
smearing_width : 0.15
xc_functional : RPBE
no-on-ni001.cell
%BLOCK LATTICE_CART
3.5240000000 0.0000000000 0.0000000000
0.0000000000 3.5240000000 0.0000000000
0.0000000000 0.0000000000 23.0000000000
%ENDBLOCK LATTICE_CART
%BLOCK POSITIONS_ABS
Ni 1.762000 0.000000 1.762000
Ni 0.000000 1.762000 1.762000
Ni 0.000000 0.000000 3.524000
Ni 1.762000 1.762000 3.524000
Ni 1.762000 0.000000 5.286000
Ni 0.000000 1.762000 5.286000
N 1.7620 0.0000 7.0196
O 1.7620 -0.0000 8.1902
%ENDBLOCK POSITIONS_ABS
%BLOCK IONIC_CONSTRAINTS
1 Ni 1 1 0 0
2 Ni 1 0 1 0
3 Ni 1 0 0 1
4 Ni 2 1 0 0
5 Ni 2 0 1 0
6 Ni 2 0 0 1
7 Ni 3 1 0 0
8 Ni 3 0 1 0
9 Ni 3 0 0 1
10 Ni 4 1 0 0
11 Ni 4 0 1 0
12 Ni 4 0 0 1
13 Ni 5 1 0 0
14 Ni 5 0 1 0
15 Ni 5 0 0 1
16 Ni 6 1 0 0
17 Ni 6 0 1 0
18 Ni 6 0 0 1
%ENDBLOCK IONIC_CONSTRAINTS
FIX_ALL_CELL : True
KPOINTS_MP_GRID : 2 2 1
KPOINTS_MP_OFFSET : 0.25 0.25 0.25
gasphase.cell
%BLOCK LATTICE_CART
3.5240000000 0.0000000000 0.0000000000
0.0000000000 3.5240000000 0.0000000000
0.0000000000 0.0000000000 23.0000000000
%ENDBLOCK LATTICE_CART
%BLOCK POSITIONS_ABS
N 1.7620 0.0000 7.0196
O 1.7620 -0.0000 8.1902
%ENDBLOCK POSITIONS_ABS
FIX_ALL_CELL : True
KPOINTS_MP_GRID : 2 2 1
KPOINTS_MP_OFFSET : 0.25 0.25 0.25
gasphase.param
task: SinglePoint
spin_polarized : True
cut_off_energy : 400.0
elec_energy_tol : 1e-07
fix_occupancy : False
iprint : 1
max_scf_cycles : 200
metals_method : dm
mixing_scheme : Pulay
nextra_bands : 10
num_dump_cycles : 0
opt_strategy_bias : 3
smearing_scheme : Gaussian
smearing_width : 0.1
xc_functional : RPBE
The workflow is as follows:
- Calculate reference states (gasphase.check). These can be ground state Kohn-Sham states or themselves excited KS states
- Calculate the ground state of NO on Ni(001)
- Calculate the leDeltaSCF excitation
We calculate a charge transfer from the molecule to the surface by removing an electron from the HOMO in the majority spin channel
- WARNING
-
A sufficient number of virtual states in the calculation, controlled by the keyword nextra_states, is very important. The more virtual states are used explicitly, the more complete is the projection onto the space of KS states. Sometimes states are almost degenerate and we also need to constrain the occupation of the other state to ensure that the population doesn\'t just switch between the two. In some cases, convergence can be very slow and a large number of SCF steps is necessary.
The resulting excitation energy is 0.46 eV.
We can calculate an intramolecular triplet excitation from HOMO to LUMO with the following constraint sequence in \<seed>.deltascf. This excites 1 electron from the HOMO in the majority spin channel to the LUMO in the minority spin channel.
The resulting excitation energy is 9.17 eV.