3. Parameters for auto-kappa

3.1. Recommendations for parameters

Table 3.1.1 Default and recommended parameters for VASP

Option name	High-throughput (default)	Accurate calculation	Related variable
k_length	20	≈40	k-mesh density for VASP
nsw_params	100	≥100	NSW parameter for the relaxation calculation
volume_relaxation	1	1	Relaxation calculation with the Birch-Murnaghan equation of sate
max_natoms	150	≥200	Number of atoms in supercell
cutoff_cubic	4.3	≥5.0	Cutoff distance for cubic FCs (Angstrom)
min_nearest	3	≥5	Cutoff distance for cubic FCs

3.2. Brief description

Please see Detailed description for details of each parameter.

Input/Output

• --file_structure, --otudir: Input structure and output directories

Parallel calculations and commands

• nprocs, mpirun: Parameters for parallel calculations

• command_{vasp/vasp_gam/alm/anphon/anphon_ver2}: Commands for VASP and ALAMODE

Accuracy

• k_length: k-point mesh for VASP calculations (official page)

• nsw_params: NSW for relaxation calculations

• cutoff_cubic, min_nearest: Cutoff distance for cubic FCs in unit of Å or nearest neighbors

• volume_relaxation: Whether to perform relaxation calculation with the Birch-Murnaghan equation of state

Supercell size

• analyze_with_larger_supercell, max_loop_for_largesc: Whether to analyze with larger supercells when imaginary frequencies occur, and the maximum number of loops

• max_natoms, delta_max_natoms: Maximum number of atoms allowed in supercells

Displacement

• nmax_suggest: Threshold of suggested displacement patterns (\(N_{sugget}\)) for the finite-displacement approach. If \(N_{suggest}\) exceeds nmax_suggest, LASSO regression is applied.

• frac_nrandom, frac_nrandom_higher: Fractional number of random displacement patterns

• mag_harm, mag_cubic, random_disp_temperature: Displacement magnitudes for harmonic, cubic, and higher-order FCs

Beyond three phonon scattering

• scph, four: Self-consistent phonon (SCPH) approach and four-phonon scattering processes

• frac_kdensity_4ph: q-point mesh for four-phonon scattering processes

Utilities

• calculate_forces: This option is useful to analyze single material with multiple machines while auto-kappa is available on single node only. If this flag is 0, the relaxation calculation is performed and the structures with displacements are generated, but the force calculations are not performed. You can perform the force calculations with multiple machines.

• harmonic_only: Whether to calculate harmonic FCs only

Others

• nonanalytic, negative_freq, vasp_parameters

3.3. Detailed description

Parser for akrun command

usage: auto-kappa [-h] [-d DIRECTORY] [--file_structure FILE_STRUCTURE] [--outdir OUTDIR] [-n NPROCS] [--mpirun MPIRUN] [--command_vasp COMMAND_VASP]
                  [--command_vasp_gam COMMAND_VASP_GAM] [--command_alm COMMAND_ALM] [--command_anphon COMMAND_ANPHON]
                  [--command_anphon_ver2 COMMAND_ANPHON_VER2] [--nonanalytic NONANALYTIC] [--cutoff_cubic CUTOFF_CUBIC] [--min_nearest MIN_NEAREST]
                  [--nmax_suggest NMAX_SUGGEST] [--frac_nrandom FRAC_NRANDOM] [--frac_nrandom_higher FRAC_NRANDOM_HIGHER] [--mag_harm MAG_HARM]
                  [--mag_cubic MAG_CUBIC] [--negative_freq NEGATIVE_FREQ] [--volume_relaxation VOLUME_RELAXATION] [--k_length K_LENGTH]
                  [--max_natoms MAX_NATOMS] [--analyze_with_larger_supercell ANALYZE_WITH_LARGERSC] [--delta_max_natoms DELTA_MAX_NATOMS]
                  [--max_loop_for_largesc MAX_LOOP_FOR_LARGESC] [--nsw_params NSW_PARAMS] [--calculate_forces CALCULATE_FORCES]
                  [--harmonic_only HARMONIC_ONLY] [--command_dfc2 COMMAND_DFC2] [--scph SCPH] [--four FOUR] [--frac_kdensity_4ph FRAC_KDENSITY_4PH]
                  [--random_disp_temperature RANDOM_DISP_TEMPERATURE] [--vasp_parameters VASP_PARAMETERS]

Named Arguments

-d, --directory

[This option will be deprecated in future versions.] Name of the directory for the PhononDB dataset, containing files such as POSCAR-unitcell, phonopy.conf, KPOINTS-**, etc. are located. --directory or --file_structure must be given. When both of them are given, --directory takes priority over --file_structure.

--file_structure

Name of the structure file: Different kinds of format including POSCAR and CIF file can be read using Structure.from_file module in Pymatgen.core.structure.

--outdir

Output directory name [./out]

Default: './out'

-n, --nprocs

Number of processes for the calculation [2]

Default: 2

--mpirun

MPI command [mpirun]

Default: 'mpirun'

--command_vasp

Command to run vasp [vasp]

Default: 'vasp'

--command_vasp_gam

Command to run vasp_gam [vasp_gam]

Default: 'vasp_gam'

--command_alm

Command to run alm [alm]

Default: 'alm'

--command_anphon

Command to run anphon [anphon]

Default: 'anphon'

--command_anphon_ver2

Command to run anphon for 4-phonon scattering [anphon.2.0]

Default: 'anphon.2.0'

--nonanalytic

NONANALYTIC tag for Anphon calculation [2]: While the default value is 2, the value is adjusted when imaginary frequencies are present.

Default: 2

--cutoff_cubic

Cutoff distance for cubic force constants (Å) [4.3]: If the provided value is too small, the cutoff distance will be adjusted using min_nearest option.

Default: 4.3

--min_nearest

Minimum nearest neighbor atoms considered for cubic FCs [3]

Default: 3

--nmax_suggest

Threshold of suggested patterns (N_{suggest}) for the finite-displacement method [100]: If N_{suggest} exceeds nmax_suggest, LASSO regression is applied for computing cubic force constants. The default value will be changed to ‘1’ in order to always use the LASSO regression method.

Default: 100

--frac_nrandom

{frac_nrandom} = Npattern * Natom / Nfc3: - Npattern: number of generated random displacement patterns - Natom : number of atoms in a supercell - Nfc3 : number of FC3 [1.0]. {frac_nrandom} should be larger than 1/3.

Default: 1.0

--frac_nrandom_higher

Npattern * Natom / Nfc4 [0.34], - Npattern: number of generated random displacement patterns, - Natom : number of atoms in the supercell, - Nfc4 : number of FC4 See the comment for frac_nrandom option.

Default: 0.34

--mag_harm

Displacement magnitude for harmonic FCs (Å) [0.01]

Default: 0.01

--mag_cubic

Displacement magnitude for cubic FCs (Å) [0.03]

Default: 0.03

--negative_freq

Threshold for negative frequency (cm^-1) [-0.001]

Default: -0.001

--volume_relaxation

Flag for the strict structure relaxation using the Birch-Murnaghan equation of state (0.off or 1.on) [1]

Default: 1

--k_length

Length to determine k-mesh for VASP calculations [20]. The following equation is used to determine the k-mesh; N = max(1, int(k_length * |a|^* + 0.5)). 10 for large gap insulators and 100 for d metals are recommended. See the official documentation at https://www.vasp.at/wiki/index.php/KPOINTS.

Default: 20

--max_natoms

Initial maximum number of atoms in supercells [150]: If imaginary frequencies are found, the maximum limit for harmonic FCs is increased in steps of delta_max_natoms. The supercell size for cubic FCs is not changed during the simulation.

Default: 150

--analyze_with_larger_supercell

Flag for analyzing harmonic properties with larger supercells if negative frequencies are present. (0.no, 1.yes) [0]

Default: 0

--delta_max_natoms

Increasing interval of the maximum number of atoms in the supercell for calculating FC2 [50]. This option is used only when --analyze_with_largersc = 1.

Default: 50

--max_loop_for_largesc

Maximum number of loops for increasing the supercell size [1]. This option is used only when --analyze_with_largersc = 1.

Default: 1

--nsw_params

Parameters which determine NSW for relaxation calculations [200:20:20]. “{nsw_init}:{nsw_diff}:{nsw_min}”: NSW = min(nsw_min, nsw_init - nsw_diff * num_errors), where num_errors is the number of errors.

Default: '200:20:20'

--calculate_forces

For calculating forces (0: off, 1: on) [1]. If set to 1, forces are calculated. If set to 0, forces are not calculated but displacement structures are generated.

Default: 1

--harmonic_only

Calculate harmonic properties only (0.No, 1.Yes) [0]

Default: 0

--command_dfc2

Command to run ‘dfc2’ implemented in ALAMODE package. [dfc2]

Default: 'dfc2'

--scph

Flag for considering the phonon renormalization using self-consistent phonon (SCP) approach. (0. off, 1. on) [0]

Default: 0

--four

Flag for considering four-phonon scattering (0.off, 1.on) [0]. If ‘scph’ option is also set to 1, SCPH+4ph is performed. –command_anphon_ver2 must be set properly.

Default: 0

--frac_kdensity_4ph

Fractional k-point density for four-phonon scattering relative to the k-point density used in three-phonon scattering calculations [0.13].

Default: 0.13

--random_disp_temperature

Temperature for the random displacement method in high-order FC calculations [500]

Default: 500.0

--vasp_parameters

VASP parameters: For example, “ISORBIT=False,DIFFG=1e-7”