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Settings

Whether using AMSET via the command-line or python API, the primary controls are contained in the settings file or dictionary. An example AMSET settings file is given here.

The settings are grouped into sections. The description for each section and settings parameter is given below.

All settings are also controllable via command-line flags. The corresponding command-line interface options are also detailed below. Any settings specified via the command-line will override those in the settings file.

General settings

These settings control the AMSET run, including interpolation density and temperature/doping ranges.

doping

Command-line option: -d, --doping

Controls which doping levels (carrier concentrations) to calculate. Concentrations given with the unit cm–3. Can be specified directly as a comma separated list, e.g.:

1E13,1E14,1E15,1E16,1E17,1E18,1E19,1E20

Alternatively, ranges can be specified using the syntax start:stop:num_steps. For example, the same doping concentrations as above can be written::

1E13:1E20:8

Negative concentrations indicate electrons (n-type doping), positive concentrations indicate holes (p-type doping).

Default: ['1.e15', '1.e16', '1.e17', '1.e18', '1.e19', '1.e20', '-1.e15', '-1.e16', '-1.e17', '-1.e18', '-1.e19', '-1.e20']

temperatures

Command-line option: -t, --temperatures

Controls which temperatures to calculate. Temperatures given in Kelvin. Can be specified directly as a comma separated list, e.g.::

300,400,500,600,700,800,900,1000

Alternatively, ranges can be specified using the syntax start:stop:num_steps, For example, the same temperature range as above can be written::

300:1000:8

Default: [300]

interpolation_factor

Command-line option: -i, --interpolation-factor

Interpolation factor controlling the interpolation density. Larger numbers indicate greater density. The number of k-points in the interpolated band structure will be roughly equal to interpolation_factor times the number of k-points in the DFT calculation. This is the primary option for controlling the accuracy of the calculated scattering rates. Transport properties should be converged with respect to this parameter.

Default: 10

scattering_type

Command-line option: -s, --scattering-type

Which scattering mechanisms to calculate. If set to auto, the scattering mechanisms will automatically be determined based on the specified material parameters. Alternatively, a comma separated list of scattering mechanism can be specified. Options include:

  • ACD (acoustic deformation potential scattering)
  • IMP (ionized impurity scattering)
  • PIE (piezoelectric scattering)
  • POP (polar optical phonon scattering)

For example, ACD,IMP,POP. The scattering mechanism will only be calculated if all the required material parameters for that mechanism are set. See the scattering section <scattering>_ of the documentation for more details.

Default: auto

wavefunction_coefficients

Command-line option: -w, --wavefunction-coefficients

Path to wavefunction coefficients file. The coefficients can be extracted from a VASP WAVECAR using the command:

amset wave

This command also requires the vasprun.xml to be in the same folder.

Default: wavefunction.h5

use_projections

Command-line option: --use-projections

Use projections to calculate wavefunction overlap. This can often result in very poor performance, and so is not recommended.

In order to use projections, the VASP calculation must be performed with LORBIT = 11.

Default: False

scissor

Command-line option: -s, --scissor

The amount to scissor the band gap, in eV. Positive values indicate band gap opening, negative values indicate band gap narrowing. Has no effect for metallic systems.

bandgap

Command-line option: -b, --bandgap

Set the band gap to this value, in eV. Will automatically determine and apply the correct band gap scissor for the specified band gap. Cannot be used in combination with the scissor option. Has no effect for metallic systems.

Material settings

These settings control the materials properties required to calculate the scattering rates.

high_frequency_dielectric

Command-line option: --high-frequency-dielectric

The high-frequency dielectric constant, in units of ϵ0\epsilon_0. Can be given as a 3x3 tensor or a single isotropic value.

Required for: POP

static_dielectric

Command-line option: --static-dielectric

The static dielectric constant, in units of ϵ0\epsilon_0. Can be given as a 3x3 tensor or a single isotropic value.

Required for: IMP, PIE, POP

elastic_constant

Command-line option: --elastic-constant

The direction averaged elastic constant, in GPa.

Required for: ACD

deformation_potential

Command-line option: --deformation-potential

The volume deformation potential, in eV. Can be given as a comma separated list of two values for the VBM and CBM, respectively, e.g.:

8.6, 7.4

Or a single value to use for all bands in metals.

Required for: ACD

piezoelectric_coefficient

command-line option: --piezoelectric-coefficient

The direction averaged piezoelectric coefficient (unitless).

Required for: PIE

acceptor_charge

Command-line option: --acceptor-charge

The charge of acceptor defects, in units of electron charge.

Required for: IMP

Default: 1

donor_charge

Command-line option: --donor-charge

The charge of donor defects, in units of electron charge.

Required for: IMP

Default: 1

pop_frequency

Command-line option: --pop-frequency

The polar optical phonon frequency, in THz. Generally, it is ok to take the highest optical phonon frequency at the Gamma point.

Required for: POP

mean_free_path

Command-line option: --mean-free-path

Basic version of boundary scattering in which the scattering rate is set to vg/Lv_g / L, where vgv_g is the group velocity and LL is the mean free path in nm.

Required for: MFP

constant_relaxation_time

Command-line option: --constant-relaxation-time

A constant relaxation time to use as the minimum relaxation time for all k-points.

It is not recommended to use this option in conjunction with any other scattering rates. Instead, this should be used to compare against results calculated in the constant relaxation time approximation.

Required for: CRT

Performance settings

These settings control the speed and accuracy of calculated properties. In general the defaults should give converged values.

energy_cutoff

Command-line option: --energy-cutoff

The energy cut-off used to determine which bands to include in the interpolation and scattering rate calculation, in eV.

Default: 1.5

fd_tol

Command-line option: --fd-tol

The Fermi–Dirac derivative tolerance that controls which k-points to calculate the scattering for. Given as a percentage from 0 to 1. Larger values indicate that the fewer k-points will be calculated, smaller values indicate a larger portion of the Brillouin zone will be calculated.

Default: 0.05

dos_estep

Command-line option: --dos-estep

The energy step for the calculated density of states and transport density of states, in eV. Controls the accuracy of determining the position of the Fermi level and transport properties. Smaller is better but can quickly get more expensive.

Default: 0.01

symprec

Command-line option: --symprec

The symmetry finding tolerance, in Å.

Default: 0.01

nworkers

Command-line option: --nworkers

Number of processors to use. -1 indicates to use all available processors.

Default: -1

Output settings

These settings control the output files and logging.

calculate_mobility

Command-line option: --calculate-mobility/--no-calculate-mobility

Whether to calculate n- and p-type carrier mobilities. Has no effect for metallic systems where mobility is not well defined.

Default: True

separate_scattering_mobilities

Command-line option: --separate-mobility/--no-separate-mobility

Whether to report the individual scattering rate mobilities. I.e., the mobility if only that scattering mechanism were present.

Default: True

file_format

Command-line option: --file-format

The output file format. Options are: json, yaml, and txt.

Note, write_mesh=True is not supported using the txt format.

Default: json

write_input

Command-line option: --write-input/--no-write-input

Whether to write the input settings to a file called amset_settings.yaml.

Default: False

write_mesh

Command-line option: --write-mesh/--no-write-mesh

Whether to write the full k-dependent properties to disk. Properties include the band energy, velocity and scattering rate. Only k-points in the irreducible wedge are included.

Note: for large values of interpolation_factor his option can use a large amount of disk space.

Default: False

Command-line option: --print-log/--no-log

Whether to print log messages.

Default: True