[ Identification | Description | Input parameters | Links ]
MCViNE_Phonon_CoherentInelastic_PolyXtal ComponentPowder average of the coherent one-phonon cross section, computed from phonon energies and polarization vectors tabulated on a grid over one reciprocal cell (MCViNE IDF format, e.g. from phonopy via MCViNE tools). A random branch and a random Q vector in a cube are drawn until the event is kinematically allowed; phonon creation/annihilation, Bose factor and Debye-Waller factor included. Scattering coefficient: total coherent cross section / Vc. Transport (same as MCViNE HomogeneousNeutronScatterer): on the first passage the neutron is forced to scatter at a uniformly chosen depth, weighted by path length, attenuation exp(-(mu+sigma)x) and the scattering coefficient; on exit it is attenuated by exp(-(mu+sigma)L_out). With order>1 further scatterings are sampled analogically (truncated exponential). With p_transmit>0 that fraction of events is kept as the attenuated direct beam. mu(v) = absorption_coefficient*2200/v. Events for which the kernel cannot scatter (kinematically forbidden) are absorbed. Geometry: box (xwidth,yheight,zdepth), cylinder (radius,yheight), hollow cylinder (+thickness) or sphere (radius only). All vectors (Q, targets, reciprocal vectors, atom positions) are in the component's local frame. Uses the shared runtime share/mcvine-lib.h/.c. Example: MCViNE_Phonon_CoherentInelastic_PolyXtal(idf_dir="MCViNE/fcc_toy_phonons", atoms="MCViNE/fcc_toy_atoms.dat", T=300, max_omega=45, radius=0.01, yheight=0.05)
| Name | Unit | Description | Default | |
| idf_dir | str | Directory with MCViNE IDF phonon files: Qgridinfo, Omega2, Polarizations[, DOS] | 0 | |
| atoms | str | Atoms file: one row per atom 'x y z mass b_coh sigma_inc sigma_abs' ([AA] cartesian, [amu], [fm], [barn], [barn]), same order as in the IDF files | 0 | |
| T | K | Temperature | 300 | |
| dw_core | AA^2 | Debye-Waller core; <0: computed from the DOS (idf_dir/DOS or dos) | -1 | |
| dos | str | Optional DOS file for the Debye-Waller factor (default: idf_dir/DOS) | 0 | |
| Vc | AA^3 | Unit cell volume; 0: (2pi)^3/|b1.(b2 x b3)| from Qgridinfo | 0 | |
| max_omega | meV | Maximum phonon energy | 50 | |
| min_omega | meV | Phonons below this energy are skipped | 0.01 | |
| unbiased | 1 | 0: MCViNE sampling (rejection + empirical accessible reciprocal volume, a few % high in tests). 1: single Q sample in the cube with its exact volume, unbiased | 0 | |
| radius | m | Outer radius of a cylinder (with yheight) or of a sphere (yheight=0) | 0 | |
| xwidth | m | Width of a box sample | 0 | |
| yheight | m | Height of a box or cylinder sample | 0 | |
| zdepth | m | Depth of a box sample | 0 | |
| thickness | m | Wall thickness of a hollow cylinder (0: filled) | 0 | |
| pack | 1 | Packing factor (scales absorption and scattering coefficients) | 1 | |
| p_transmit | 1 | Monte Carlo fraction of events kept as unscattered transmitted beam (0: always scatter) | 0 | |
| order | 1 | Maximum number of scattering events per neutron (1: single scattering) | 1 |
| AT ( | , | , | ) RELATIVE | |||
|---|---|---|---|---|---|---|
| ROTATED ( | , | , | ) RELATIVE |
MCViNE_Phonon_CoherentInelastic_PolyXtal.comp.
[ Identification | Description | Examples | Input parameters | Links ]
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