We also simulate the VFF composite-pulse nutation (the first-pulse length is variable whereas the other two are constant) using SIMPSON version 1.1.1, a general simulation program for solid-state NMR spectroscopy provided by M. Bak, J. T. Rasmussen, and N. C. Nielsen, J. Magn. Reson. 147, 296-330 (2000).

Due to different conventions for the definition of the asymmetry parameter used in SIMPSON and the Java applets, these two approaches provide different simulations. Fortunately, as proposed by Klaus Eichele, if we add 90° to alpha, the first Euler angle in SIMPSON TCL scripts, these two approaches give identical results.

# compositevffxtal.in
# Spin-3/2 central-line intensity calculation
# for a static crystal.
# With alpha0beta0 crystal_file and
# whatever the asymmetry parameter,
# qcc = 1 MHz gives a line splitting of 500 kHz
# and a quadrupole coupling omegaQ of 250 kHz.

spinsys {
  channels 23Na
  nuclei   23Na
  quadrupole 1 1 1e6 1 90 0 0
}



par {
  proton_frequency 400e6
  spin_rate        0
  variable tsw     0.5
  sw               1.0e6/tsw
  np               41
 crystal_file      alpha0beta0
 gamma_angles      1
 start_operator    0.2*I1z
 detect_operator   I1c
 verbose           1101
 variable rf       100000
  variable p1      0
  variable p2      5
 variable p3       5
}

proc pulseq {} {
  global par
  acq

  for {set i 1} {$i < $par(np)} {incr i} {

    pulse $par(tsw) $par(rf) $par(ph1)

    store 1

    pulse $par(p2) $par(rf) $par(ph2)

    pulse $par(p3) $par(rf) $par(ph3)


    acq $par(ph31)

    Reset


    prop 1
  }
}

proc main {} {
  global par

  foreach p {{-x x  x -y}\
             {-x x -x  y}\
             { x x -x -y}\
             { x x  x  y}} {
    set par(ph1)  [lindex $p 0]
    set par(ph2)  [lindex $p 1]
    set par(ph3)  [lindex $p 2]
    set par(ph31) [lindex $p 3]

    set g [fsimpson] 
    if [info exists f] {
      fadd $f $g
      funload $g
    } else {
      set f $g
    }
  }

  fsave $f $par(name).fid
  funload $f

  puts "Larmor frequency (Hz) of 23Na: "
  puts [resfreq 23Na $par(proton_frequency)]
}
        

File name.
Description.








Spin I = 3/2.
1st-order
quadrupole
interaction,
qcc = 1 MHz,
eta = 1.


Static crystal.
0.5 µs pulse increment.

40 pulse increments.


0.2 for normalization.
Central-transition.

100 kHz RF pulse.
1st-pulse duration.
2nd-pulse duration.
3th-pulse duration.




No pulse, no signal.



1st (variable) pulse
with ph1 phase.
Save propagator.

2nd-pulse
with ph2 phase.
3th-pulse
with ph3 phase.

Receiver phase ph31.

Reset propagator to
initial value.

Recall the propagator
 at the end of 
 the 1st pulse.




RF pulse and receiver
phase cycling.
        

SIMPSON uses gyromagnetic ratios provided by IUPAC for the determination of the Larmor frequency of a nucleus. For example:

²³Na Larmor frequency = Proton Larmor frequency * ²³Na gyromagnetic ratio / Proton gyromagnetic ratio;

400 MHz * 7.0808493 / 26.7522128 = 105.8731007 MHz.