[ Identification | Description | Input parameters | Links ]

The MCViNE_Phonon_IncoherentInelastic_process Component

Union process: One-phonon incoherent inelastic scattering from a phonon DOS (incoherent approximation), optional Ef focusing.

Identification

• Author: Fahima Islam (McStas port of the MCViNE phonon IncoherentInelastic / IncoherentInelastic_EnergyFocusing kernels; MCViNE by J. Y. Y. Lin et al.)
• Origin: MCViNE, https://github.com/mcvine/mcvine (mccomponents/lib/kernels/sample/phonon/IncoherentInelastic.cc, IncoherentInelastic_EnergyFocusing.cc)
• Date: 2026-09-29

Description

S_inc(Q,E) = exp(-2W) hbar^2Q^2/(2M) g(|E|)/|E| [n(E)+1 or n(E)] with the DOS
g(E) normalised to 1, Debye-Waller factor computed from the DOS (MCViNE
DWFromDOS), and the DOS preprocessed like MCViNE (resampled to >=500 points,
parabolic low-energy fit, normalised). The final direction is uniform over 4pi;
Ef is uniform in [Ei-Emax_dos, Ei+Emax_dos]. With dEf>0, Ef is restricted to
Ef +/- dEf/2 (MCViNE IncoherentInelastic_EnergyFocusing).
DOS file: 2 columns E [meV] g(E) (a '#...THz' comment switches the unit to THz)
or an MCViNE IDF binary 'DOS' file. Multiphonon terms are not included (see
Union IncoherentPhonon_process or NCrystal for those).

Union process. Part of the Union components: define this process, collect it
into a material with Union_make_material (absorption is set there with
my_absorption, the absorption inverse penetration depth at 2200 m/s), assign
the material to Union_box/Union_cylinder/Union_sphere/Union_mesh geometries,
and add a Union_master after them. Geometry, attenuation and multiple
scattering are handled by Union_master; this component provides the MCViNE
kernel: the scattering coefficient and the final-state sampling (weight).
Isotropic process (powder/liquid-like); rotation is irrelevant.
The kernel code is shared with the standalone component MCViNE_Phonon_IncoherentInelastic (mcvine-lib.c).
Uses share/mcvine-lib.h/.c and share/mcvine-union-lib.h/.c; the process type
MCViNE is declared in share/union-lib.h and registered with Union_master in
share/mcvine-union-lib.h.

Example: MCViNE_Phonon_IncoherentInelastic_process(dos="MCViNE/Debye_dos.dat", T=300, average_mass=50.94, sigma_inc=10.1, Vc=27.6)

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
dos	str	Phonon DOS file	0
T	K	Temperature	300
average_mass	amu	Average atomic mass	0
Ef	meV	Final energy for energy focusing (used when dEf>0)	0
dEf	meV	Full width of the final-energy window; 0 disables focusing	0
sigma_inc	barn	Incoherent scattering cross section per unit cell	0
Vc	AA^3	Unit cell volume	0
packing_factor	1	Packing factor (scales the scattering coefficient)	1
interact_fraction	1	Union: fraction of interactions forced to this process (-1: by cross section)	-1
init	string	Deprecated and unused, accepted like on the other Union components (see Union_init).	""

AT (	,	,		) RELATIVE		Generate to clipboard
ROTATED (	,	,		) RELATIVE

Links

• Source code for MCViNE_Phonon_IncoherentInelastic_process.comp.
• MCViNE documentation: https://mcvine.github.io

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[ Identification | Description | Examples | Input parameters | Links ]

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Last Modified: Tuesday, 06-Oct-2026 21:19:12 CEST