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<p>Hello Anita,</p>
<p>Thanks for using iFit. My bet is that you wish to model a
Berylium filter at l-N2 temperature. <br>
</p>
<p>Your methodology seems fine, and you use the right methods. Also,
the use of Isotropic_Sqw is OK, especially with 'norm=0' to make
sure you use the raw Sqw data file.<br>
</p>
<p>But you must be aware that the phonon calculation (PhonoPy/QE)
only computes the coherent inelastic part of the scattering law.
There is no elastic (structure) data there. This data is then not
complete, and you should complement the Isotropic_Sqw component
with a PowerN component using the Be.laz file. <br>
</p>
<p>Last, I have worked to improve the handling of the detailed
balance in the component Isotropic_Sqw, which should be there for
McStas 2.5 (before Xmas). This should allow to export only the
w>=0 part of the classical S(q,w), as obtained by evaluating
the 'powder', without applying the symmetrize/deBosify/Bosify
stuff.</p>
<p>Hope these considerations help you...</p>
<p>Emmanuel.<br>
</p>
<div class="moz-cite-prefix">On 12/6/18 13:38, Anita Petrova wrote:<br>
</div>
<blockquote type="cite"
cite="mid:1544099936.624599697@f116.i.mail.ru">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
Dear Emmanuel,<br>
<br>
We are trying to make S(q,w) file for Isotropic_Sqw component in
McStas for beryllium using iFit. We have ab initio calculations as
an input file. Here I present the way we have done it:<br>
<br>
1. ab initio model calculations were transformed from monocrystal
data to powder data (function powder)<br>
2. the range for q and w was stated to get S(q,w) matrix (function
iData)<br>
3. data was symmetrized in energy (function symmetrize)<br>
4. data was debosified (function deBosify) <br>
5. data was bosified for T=80K (function Bosify)<br>
<br>
So we put it into the instrument fire and execute with the
following parameters (excluding geometrical parameters):<br>
<br>
Sqw_coh="Be_data_T80_final.sqw",<br>
Sqw_inc="",<br>
T=0,<br>
p_interact=-1,<br>
sigma_coh=7.63,<br>
sigma_inc=0.00181,<br>
verbose=1,<br>
classical=0,<br>
norm=0<br>
<br>
We tried different values of norm with different thickness of the
Be sample, and the results are unphysical. Find attached the
results of ab initio calculations and the final sample file.<br>
<br>
Could you please provide any help?<br>
<br>
<br>
Sincerely,<br>
Anita Petrova<br>
<br>
Saint-Petersburg State University<br>
Petergof, St.-Petersburg, Russia<br>
phone: <span><span><span><span><span><span
class="js-phone-number">+7(9817) 96-95-87</span></span></span><span><span><span><span><span><span
class="js-phone-number"></span></span></span></span></span></span></span></span></span><br>
e mail: <a href="mailto:ani_petrova@mail.ru" target="_blank"
rel=" noopener noreferrer" moz-do-not-send="true">ani_petrova@mail.ru</a>
<br>
</blockquote>
<pre class="moz-signature" cols="72">--
Emmanuel FARHI, \|/ ____ \|/
Spectroscopy Group Institut Laue-Langevin (ILL) Grenoble ~@-/ oO \-@~
71 av des Martyrs,CS 20156,38042 Grenoble Cedex 9,France /_( \__/ )_\
Work :Tel (33/0) 4 76 20 71 35. Fax (33/0) 4 76 48 39 06 \__U_/
</pre>
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