phonons_only
| Format: | phonons_only T |
| Description: | Will perform only phonons calculations on the supplied k-point mesh. |
| Examples: | phonons_only T |
| Default: | False |
do_dispersion
| Format: | do_dispersion N1 N2 R1 R2 R3 R4 R5 R6 … |
| Description: | Will perform dispersion calculations using supplied path in the Brillouin zone. The first natural number N1 specifies the number of path elements, and second (N2) tells how many point to use on every element. Each portion of the path is specified by the first and last point in the reciprocal space in the basis frame. There should be exactly N1 lines with the first path portion specifications. |
| Examples: | do_dispersion 2 100 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.0 |
| Default: | False |
Iterations
| Format: | Iteration L |
| Description: | Turns on iterative solution to to the BTE. Default value is .True., thus this is the default approach. The first step in the iterative solution produces relaxation time approximation (RTA), this if the variable iter_steps is set to 1 (default), then RTA solution is produced. By setting the number iteration steps to desired value, full iterative solution is recovered. Iterative solution typically has greater thermal conductivity than RTA, since it is properly treats normal phonon-phonon scattering processes as non-resistive. If Iterations is set to false, then variational solution is produced (for versions after PhonTS.1.1.0, default temperature gradient is along z-axis of the supplied cell). In our experience, there is no universally good set of trial functions that can produce solutions close to the iterative approach. Currently, the maximum set of the trial functions consists of 55 Chebyshev polynomials in terms of compunents of the k-vector of the increasing order, as described in here. Since convergence with respect to basis set is somewhat slow, default is set to 18. Typically, the result is on par with RTA. The number of the variational functions might be controlled from the input file, but currently no different choices of the trial functions is possible. The only exception is a possibility of finishing up iterative run using relatively few steps (~5) with variational calculations in which subsequent approximations for the deviation from the equilibrium distribution is used as a variational trial functions (set by var_finish keyword). |
| Examples: | Iteration False |
| Default: | True |
QHA
| Format: | QHA L N R |
| Description: | Turns on iterative solution to to the BTE. Default value is .True., thus this is the default approach. The first step in the iterative solution produces relaxation time approximation (RTA), this if the variable iter_steps is set to 1 (default), then RTA solution is produced. By setting the number iteration steps to desired value, full iterative solution is recovered. Iterative solution typically has greater thermal conductivity than RTA, since it is properly treats normal phonon-phonon scattering processes as non-resistive. If Iterations is set to false, then variational solution is produced (for versions after PhonTS.1.1.0, default temperature gradient is along z-axis of the supplied cell). In our experience, there is no universally good set of trial functions that can produce solutions close to the iterative approach. Currently, the maximum set of the trial functions consists of 55 Chebyshev polynomials in terms of compunents of the k-vector of the increasing order, as described in here . Since convergence with respect to basis set is somewhat slow, default is set to 18. Typically, the result is on par with RTA. The number of the variational functions might be controlled from the input file, but currently no different choices of the trial functions is possible. The only exception is a possibility of finishing up iterative run using relatively few steps (~5) with variational calculations in which subsequent approximations for the deviation from the equilibrium distribution is used as a variational trial functions (set by var_finish keyword). |
| Examples: | QHA T 10 0.02 |
| Default: | False |
do_gruneisen
| Format: | do_gruneisen L |
| Description: | Do a calculation od the gruneisen parameter from the perturbation theory (Under construction). |
| Examples: | do_gruneisen T |
| Default: | False |
optimize
| Format: | Optimize L |
| Description: | Performs full potential energy minimation. Only applicable for the classical potentials that are implemented within PhonTS. |
| Examples: | Optimize T |
| Default: | False |
single_kpoints
| Format: | single_kpoints R1 R2 R3 |
| Description: | With this keyword, the phonon lifetimes at a single k-point is calculated. The k-point shall be provided in reciprocal space basis frame. This keyword can be used, for example, in order to calculate the linewidth of the phonon states at the gamma-point, which for optical phonons corresponds to the Raman or IR linewidth. |
| Examples: | single_kpoints 0.0 0.0 0.0 |
| Default: | Not set |
VCA
| Format: | VCA N1 N2 |
| Description: | This keyword sets up Virtual Crystal Approximation for phonons. It is similar in spirit to the same approximation for electrons, to treat alloyed systems, but applied to phonons. Alloy is treated as a virtual ideal crystal with masses being the average mass of the constituents (appropriately weighted) and the interaction between atoms being the average of the constituents in the same structure as well. For phonons, this means average second and third order force constants. To restore the actual crystal, a mass disorder term is added to the scattering (force constant disorder is currently neglected). To set up the VCA calculations one has to do the following: 1. Define all species (using species keyword) that will be present in the system with appropriate masses/charges 2. Define the host lattice via cell/vectors and atoms keywords. 3. VCA keywords parameters have the following meaning: N1 tells PhonTS how many atomic types will experience the disorder, thus N1 lines will follow this line. N2 tells PhonTS how many different atom types will form current average atom C1…CN2 lists these atom types, C1 will be the atom name that is replaced with the average atoms, and thus it ought to appear within a structure. R1…RN2 then lists concentrations of the corresponding substitutes. These numbers have to add to unity. VCA calculations are available for both ab initio and classical potentials. In the former case, Phons will create a number of the structure files whose names will reflect the atoms involved. |
| Examples: | VCA 1 2 Ca Mg 0.1 0.9 |
| Default: | Not set |