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:

ADP (acoustic deformation potential scattering)
IMP (ionized impurity scattering)
PIE (piezoelectric scattering)
POP (polar optical phonon scattering)
CRT (constant relaxation time)
MFP (mean free path scattering)

For example, ADP,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.

`zero_weighted_kpoints`¶

Command-line option: -z, --zero-weighted-kpoints

How to handle "zero-weighted" k-points if they are present in the calculation. Options are:

keep: Keep zero-weighted k-points in the band structure.
drop: Drop zero-weighted k-points, keeping only the weighted k-points.
prefer: Drop weighted-kpoints if zero-weighted k-points are present in the calculation (useful for cheap hybrid calculations).

`free_carrier_screening`¶

Command-line option: --free-carrier-screening

Whether free carriers will screen polar optical phonon and piezoelectric scattering rates. This modifies the matrix elements from a $\frac{1}{\left | \mathbf{q} + \mathbf{G} \right |}$ dependence to a $\frac{1}{\left | \mathbf{q} + \mathbf{G} \right | + \beta_\infty}$ dependence, where $\beta_\infty$ is the inverse screening length that depends on the temperature, carrier concentration, and high-frequency dielectric constant.

This can result in a large reduction in the scattering rates at high carrier concentrations.

Default: False

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 $\epsilon_0$ . Can be given as a 3x3 tensor or a single isotropic value.

Required for: POP, PIE

`static_dielectric`¶

Command-line option: --static-dielectric

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

Required for: IMP, POP

`elastic_constant`¶

Command-line option: --elastic-constant

The elastic constants as the full 3x3x3x3 tensor or 6x6 Voigt form, in GPa.

Alteratively, a single averaged value can be given (not recommended).

Required for: ADP, PIE

`deformation_potential`¶

Command-line option: --deformation-potential

Path to file containing deformation potentials for all bands, generated using amset deform read.

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

8.6, 7.4

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

Required for: ADP

`piezoelectric_constant`¶

command-line option: --piezoelectric-constant

The piezoelectric constants ( $\mathbf{e}$ ) in C/m² given as either the full 3x3x3 tensor or the 3x6 Voigt form.

Required for: PIE

`defect_charge`¶

Command-line option: --defect-charge

The charge of defects, in units of electron charge.

Note: donor_charge and acceptor_charge were amalgamated into a single setting in version 0.5.0.

Required for: IMP

Default: 1

`compensation_factor`¶

Command-line option: --compensation-factor

The amount of defect compensation to include.

The total impurity concentration is calculated as compensation_factor $\times (n_0 - p_0) / q$ , where $(n_0 - p_0)$ is the concentration of excess donors or acceptors and $q$ is the defect charge.

Required for: IMP

Default: 2

`pop_frequency`¶

Command-line option: --pop-frequency

The polar optical phonon frequency, in THz. This can be generated from a VASP DFPT calculation using amset phonon-frequency.

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 $v_g / L$ , where $v_g$ is the group velocity and $L$ 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.

When using multiprocessing it is recommended to run export OMP_NUM_THREADS=1 before running amset.

Default: -1

`cache_wavefunction`¶

Command-line option: --cache-wavefunction

Cache interpolated wavefunction coefficients. This means that the coefficients for each band and k-point on the Fourier interpolated k-point mesh are only calculated once. While this can yield a significant speed-up, it also massively increases memory requirements, especially if using a low value of fd_tol, or if the system contains very flat bands.

If memory issues occur, it is recommended to set cache_wavefunction to False.

Default: True

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

`print_log`¶

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

Whether to print log messages.

Default: True

Settings¶

General settings¶

doping¶

temperatures¶

interpolation_factor¶

scattering_type¶

wavefunction_coefficients¶

use_projections¶

scissor¶

bandgap¶

zero_weighted_kpoints¶

free_carrier_screening¶

Material settings¶

high_frequency_dielectric¶

static_dielectric¶

elastic_constant¶

deformation_potential¶

piezoelectric_constant¶

defect_charge¶

compensation_factor¶

pop_frequency¶

mean_free_path¶

constant_relaxation_time¶

Performance settings¶

energy_cutoff¶

fd_tol¶

dos_estep¶

symprec¶

nworkers¶

cache_wavefunction¶

Output settings¶

calculate_mobility¶

separate_scattering_mobilities¶

file_format¶

write_input¶

write_mesh¶

print_log¶

`doping`¶

`temperatures`¶

`interpolation_factor`¶

`scattering_type`¶

`wavefunction_coefficients`¶

`use_projections`¶

`scissor`¶

`bandgap`¶

`zero_weighted_kpoints`¶

`free_carrier_screening`¶

`high_frequency_dielectric`¶

`static_dielectric`¶

`elastic_constant`¶

`deformation_potential`¶

`piezoelectric_constant`¶

`defect_charge`¶

`compensation_factor`¶

`pop_frequency`¶

`mean_free_path`¶

`constant_relaxation_time`¶

`energy_cutoff`¶

`fd_tol`¶

`dos_estep`¶

`symprec`¶

`nworkers`¶

`cache_wavefunction`¶

`calculate_mobility`¶

`separate_scattering_mobilities`¶

`file_format`¶

`write_input`¶

`write_mesh`¶

`print_log`¶