# 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/m^{2} 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`