Simulation of slow-motional cw EPR spectra
chili(Sys,Dyn,Exp) spec = chili(...) [B,spec] = chili(...) ... = chili(Sys,Dyn,Exp,Opt)
See also the tutorial on how to use chili
.
chili
computes cw EPR spectra of systems with
one unpaired electron and one or more nuclei in the slow-motional
regime.
Up to four input arguments are accepted:
Sys
: static parameters of the spin system
Dyn
: dynamic parameters of the spin system
Exp
: eperimental parameters
Opt
: options and settings
If no input argument is given, a short help summary is shown (same
as when typing help chili
).
Up to two output arguments are returned:
B
: magnetic field axis vector, in mT
spc
: spectrum
If no output argument is given, chili
plots the spectrum.
Sys
is a structure containing the parameters of
the spin system. Only S=1/2 systems
are supported. Used parameters are g
, gpa
,
Nucs
, A
, Apa
. See the documentation
on spin system structures for details.
The nuclear quadrupole interaction is not included in the computation.
Dyn
is a structure collecting values for dynamic parameters
of the spin system. The following parameters are possible:
tcorr |
Scalar Rotational correlation time for isotropic rotational diffusion, in seconds. If tcorr is set, Diff is ignored.
For isotropic rotational motion, the correlation time |
Diff |
Scalar or 2-element vector Rotational diffusion rates (principal values of the rotational diffusion tensor), in second^-1. Scalar: isotopic diffusion, 2-element vector: axial diffusion tensor with [Dxy Dzz] .
Diff is ignored if tcorr is given.
|
Diffpa |
3-element vector Euler angles describing the orientation of the rotational diffusion tensor in the molecular frame. |
lw |
Scalar Residual line width (Lorentzian FWHM), in Hz. |
Exchange |
Scalar Heisenberg spin exchange frequency, in Hz. |
Exp
contains the following experimental parameters.
mwFreq | Spectrometer frequency in GHz |
nPoints | Number of points along field axis (default 1024) |
CenterSweep | 2-element vector [center sweep] with center field center and full field sweep range sweep , both in mT.
If both CenterSweep and Range are not specified, the magnetic field range is automatically determined to cover the full spectral range. |
Range | 2-element vector [minField maxField] with lower and upper limit
of field scan range in mT.
Range is only used if CenterSweep is not given.
If both CenterSweep and Range are not specified, the magnetic field range is automatically determined to cover the full spectral range.
|
Harmonic | Detection harmonic (0, 1 or 2), default is 1. |
Opt
, the options structure, collects all settings relating to
the algorithm used and the behaviour of the function. The following fields
are available:
LLKM |
4-element vector [evenLmax oddLmax Kmax Mmax] Specifies the basis size by giving the maximum values for, in that order, even L, odd L, M and K. M and K must be less than or equal to the maximum value of L. If this field, is not specified, chili sets the basis size
automatically. This is adequate for most, but not all, cases.
|
Verbosity |
0 (default), 1 Determines how much information chili prints to the screen. If
Opt.Verbosity=0 , is is completely silent. 1 prints details about
the progress of the computation.
|
The cw EPR spectrum of a slow tumbling nitroxide radical can be simulated with the following lines.
Sys = struct('g',[2.008 2.0061 2.0027],'Nucs','14N','A',[16 16 86]); Exp = struct('mwFreq',9.5); Dynamics = struct('lw',0.01,'tcorr',32e-9); chili(Sys,Dynamics,Exp);
chili
solves the Stochastic Liouville equation in an eigenbasis
of the diffusion operator. The eigenfunctions are normalized Wigner rotation
functions DLK,M(Ω) with -L≤K,M≤L. The number
of basis functions is determined by maximum values of even L, odd L, K and M.
The larger these values, the larger the basis and the more accurate the spectrum.
chili
computes EPR line positions to first order. For the diffusion,
both secular and nonsecular terms are included.
If the spin system contains more than one nucleus, only the first nucleus is included in the full SLE simulation. The effect of all the others is added by post-convolution: The isotropic stick spectrum due to all other nuclei is simulated and the used to convole the SLE-simulated spectrum of the first nucleus.
For full details of the method see