SIMPSON coding examples

SIMPSON Tutorial #2: Magic-Angle spinning

by Thomas Vosegaard

This exercise is similar to Tutorial 1 but now the sample is spinning. The spin rate is controlled by the spin_rate in the par section of the input file.

  1. Try to run the input file 2_MAS.in (2_MAS,1.spe)
  2. Change the CSA and asymmetry parameter and observe the spectrum (2_MAS,2.spe). Eventually compare with the powder spectra simulated in Tutorial 1.
  3. Change the spin rate and observe the result.

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spinsys {
  channels 1H
  nuclei 1H
  shift 1 0 10p 0 0 0 0
}

par {
  spin_rate        1000
  variable index   1

  np               2048
  proton_frequency 400e6
  start_operator   I1x
  detect_operator  I1p
  method           direct
  crystal_file     rep30
  gamma_angles     8
  sw               20000
  variable tsw     1e6/sw
  verbose          1101
}

proc pulseq {} {
  global par
  
  acq_block {
    delay $par(tsw)
	}
}

proc main {} {
  global par
  
  set f [fsimpson]
  faddlb $f 30 0
  fsave $f $par(name),$par(index).fid
  fzerofill $f 8192
  fft $f
  fsave $f $par(name),$par(index).spe -binary
}
Files:2_MAS,1.spe  preview
2_MAS,2.spe  preview
2_MAS.in
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Comment on SIMPSON Tutorial #2: Magic-Angle spinning

by Thomas Vosegaard

The powder averaging in this example is probably not sufficient. I would expect that the crystallite file rep168 will provide a converged spectrum.
In addition, you see that some of the spinning sidebands are negative. This is typically the case when there are not enough gamma angles. In the attached file, I have used 16 gamma angles, and there are no negative spinning sidebands.

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par {
  ...
  gamma_angles 16
  ...
}
File:2_MAS,3.spe  preview
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