The `Phonon_BvK_PG` Component

A sample for phonon scattering based on cross section expressions from the Boothroyd textbook based upon the algorithm from component Phonon_simple (with expressions from Squires, Ch. 3) Using the Born-von Karman force constnts and the normal mode formalism

Identification

Author: Kim Lefmann
Origin: NBI, KU
Date: 06.12.2025

Description

Single-cylinder or slap shaped shape.
Absorption included.
No multiple scattering.
No incoherent scattering emitted, but incoherent is present in attenuation
No attenuation from coherent scattering. No Bragg scattering.
Specialized for Pyrolytic Graphite (PG)

Algorithm:
0. Always perform the scattering if possible (otherwise ABSORB)
1. Choose direction within a focusing solid angle
2. Select a phonon mode at random (alternatively mode number fixed by user)
3. Calculate the zeros of (E_i-E_f-hbar omega(kappa)) as a function of k_f
4. Choose one value of k_f (there always at least one possible; see e.g. Squires)
5. Perform the correct weight transformation
For details: see article A. F. Davidsen et al, manuscript for J Neutron Res 2026

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
hh	rlu	h-coordinate (in units of a*) of the q-point used when calculating the dispersion	0
kk	rlu	k-coordinate (in units of a*) of the q-point used when calculating the dispersion	0
ll	rlu	l-coordinate (in units of c*) of the q-point used when calculating the dispersion	0
radius	m	Outer radius of sample in (x,z) plane	0
xwidth	m	Horiz. dimension of sample if slap	0
yheight	m	Height of sample in y direction	0
zdepth	m	Depth of sample if slap	0
sigma_abs	barns	Absorption cross section at 2200 m/s per atom	0
sigma_inc	barns	Incoherent scattering cross section per atom	0
DW	1	Debye-Waller factor; scalar value (no q-dependence)	1
T	K	Temperature
focus_r	m	Radius of sphere containing target.	0
focus_xw	m	horiz. dimension of a rectangular area	0
focus_yh	m	vert. dimension of a rectangular area	0
focus_aw	deg	horiz. angular dimension of a rectangular area	0
focus_ah	deg	vert. angular dimension of a rectangular area	0
target_x	m	position of target to focus at . Transverse coordinate	0
target_y	m	position of target to focus at. Vertical coordinate	0
target_z	m	position of target to focus at. Straight ahead.	0
target_index	1	relative index of component to focus at, e.g. next is +1	0
mode_input	1	order of the phonon mode to be scattered (unphysical). In the range 0 through 11 . If mode_input == 12, then the mode is choosen at random
e_steps_low	1	Amount of possible intersections beneath the elastic line
e_steps_high	1	Amount of possible intersections above the elastic line
verbose_input	1	toggles verbose mode (verbose>1) or eigenvector mode (verbose==1)	0
dispersion	1	0: do nothing special; 1: calculate and output the dispersion; 2: calculate and output the dispersion while varying v_f	0

AT (	,	,		) RELATIVE
ROTATED (	,	,		) RELATIVE

The Phonon_BvK_PG Component

Identification

Description

Input parameters

Links

The `Phonon_BvK_PG` Component