Internal S(Q, E) Models

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Internal S(q,E) models include the following:

Elastic Model

The elastic S(Q, E) model consists of a list of elastic peaks which are used to simulate Bragg tails. Each line defines a peak, with the columns of each line being: h, k, l, q width, E width, and S.

Here's a sample input file defining three Bragg peaks:

1 0 0    0.002 0.01    0.5
1 1 0    0.002 0.01    1
2 2 0    0.002 0.01    5

Tabulated Model

This model loads a table of S(Q, E) points in the four-dimensional (Q, E) space and constructs a kd-tree out of it. As with the "elastic model" each line defines one point. The columns are h, k, l, E, and S.

Here's a (very unrealistic) sample input file defining three points. A realistic input file would include tens of thousands of points to cover a fine and large enough grid in (Q, E) space.

1 0 0    0    1
1 0 0  0.5    0.5
1 0 0 -0.5    0.5

Simple Phonon Model

With the simple phonon model sinusoidal phonon branches can be defined around a given Bragg peak.

In the following input file we define a longitudinal [110] and two transverse ([001] and [1-10]) branches around the (440) peak:

G               = 4,  4, 0
TA1             = 0,  0, 1
TA2             = 1, -1, 0

LA_amp          = 25
LA_freq         = 0.5*pi/sqrt(2)
LA_E_HWHM       = 0.1
LA_q_HWHM       = 0.05
LA_S0           = 1

TA1_amp         = 15
TA1_freq        = 0.5*pi
TA1_E_HWHM      = 0.2
TA1_q_HWHM      = 0.025
TA1_S0          = 1

TA2_amp         = 10
TA2_freq        = 0.5*pi/sqrt(2)
TA2_E_HWHM      = 0.2
TA2_q_HWHM      = 0.025
TA2_S0          = 1

Simple Magnon Model

The simple magnon model creates quadratic (ferromagnetic) or linear (antiferromagnetic) branches spherically around a given Bragg peak. (Note that this model is not to be confused with the more advanced magnon calculator.)

In the following input file we define magnons with a stiffness of D=20 around the (110) peak:

disp            = 0
G               = 1,  1, 0

D               = 20
offs            = 0.
E_HWHM          = 0.05
q_HWHM          = 0.05
S0              = 1

num_points      = 50