mirror of https://github.com/phonopy/phono3py.git
70 lines
2.7 KiB
Markdown
70 lines
2.7 KiB
Markdown
This is the example of the wurtzite-type AlN phono3py calculation. The VASP code
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was used with 500 eV and LDA as XC functional. The experimental lattice
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parameters were used and the internal positions of atoms were relaxed by
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calculation. The 3x3x2 and 5x5x3 supercells were chosen for fc3 and fc2. The
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6x6x4, 2x2x2, 1x1x2 k-point sampling meshes with Gamma-centre in the basal plane
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and off-Gamma-centre along c-axis were employed for the unit cell, fc3
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supercell, and fc2 supercell, respectively. For the DFPT calculation of Born
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effective charges and dielectric constant, the 12x12x8 k-point sampling mesh
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with the similar shift was used.
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Then the forces were calculated with the above settings. `FORCES_FC3` and
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`FORCES_FC2` were created with subtracting residual forces of perfect supercell
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from all displaced supercell forces.
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Perfect and displaced supercells were created by
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```bash
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% phono3py --dim 3 3 2 -c POSCAR-unitcell -d
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```
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In the example directory, `FORCES_FC3` is compressed to `FORCES_FC3.xz`. After
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unzipping `FORCES_FC3.xz` (e.g., using `xz -d`), to obtain `fc3.hdf5` and
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`fc2.hdf5` using symfc (the results without using symfc, i.e., finite difference
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method, are shown at the bottom of this README)
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```bash
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% phono3py-load --symfc -v
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```
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Lattice thermal conductivity is calculated by
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```bash
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% phono3py-load --mesh 40 --br --ts 300
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```
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`kappa-m15158.hdf5` is written as the result. Parameters for non-analytical term
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correction (NAC) is automatically read from those stored in `phono3py_disp.yaml` or
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`BORN` file. The lattice thermal conductivity is calculated as k_xx=242.8 and
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k_zz=226.5 W/m-K at 300 K. Without NAC, k_xx=233.6 and k_zz=222.2.
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Use of larger supercell for fc2 may change the shape of phonon band structure.
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To see it, first regenerate `phono3py_disp.yaml` with `--dim-fc2` option,
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```bash
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% phono3py --dim 3 3 2 --dim-fc2 5 5 3 -c POSCAR-unitcell -d
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```
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Then re-create force constants and calculate thermal conductivity,
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```bash
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% phono3py-load --symfc -v
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% phono3py-load --br --mesh=40 --ts 300
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```
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If `phono3py_disp.yaml` is renamed to `phono3py_disp_dimfc2.yaml`, it can be
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specified at the first argument of `phono3py-load` command:
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```bash
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% phono3py-load phono3py_disp_dimfc2.yaml --symfc -v
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% phono3py-load phono3py_disp_dimfc2.yaml --br --mesh=40 --ts 300
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```
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k_xx=240.2 and k_zz=230.1 are obtained. In the case of this example, we can see
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that the larger fc2 supercell contributes little, which means that the 3x3x2
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supercell was good enough to obtain a good shape of phonon band structure.
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Using the finite difference method implemented in phono3py, lattice thermal
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conductivities are obtained as k_xx=251.2 and k_zz=233,4 without using the large
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fc2 supercell and k_xx=249.4 k_zz=236.9 using the large fc2 supercell.
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