Problems with dipolar coupling
Christian Bretschneider
we would like to use Spinevolution to verify some of our analytical
calculations. Considering liquid states, we have a homonuclear three
spin-system (I_1,I_2,I_3) forming a molecule (triangle), in which the
distances and angles are well-known. We would like to simulate the
time evolution of certain coherences (like I1zI2z) in the presence of
the following Hamiltonian (H = H_cs + H_j + H_d). Thereby it is
important to suppress the effects of dipolar interactions between the
molecules and focus only on the interactions inside the molecule. But
I don't know how to tell the programme to do so.
For example, setting I1zI2z as the initial term and check if the
coherence stays constant or oscillates over time. And if so, which
other coherences are being populated. It seems to work fine, if I
deactivate the dipolar interaction in triangle.dip. But as soon as I
use the dipolar interaction something goes badly wrong.
Questions:
-Is Spinevolution still working in liquid states, if I enter a value
in the atomic_coords folder or does it switch to solid state?
-Can I somehow adjust the tumbling motion of molecules in
Spinevolution?
I hope this was all reasonably comprehensive and I haven't overlooked
something trivial.
Thanks in advance,
Christian
****** The System ********************************************
spectrometer(MHz) 500
spinning_freq(kHz) *
channels H1
nuclei H1 H1 H1
atomic_coords triangle.cor
cs_isotropic 0 -600 -400 Hz
csa_parameters *
j_coupling 1 2 10
j_coupling 1 3 20
j_coupling 2 3 2
quadrupole *
dip_switchboard triangle.dip
csa_switchboard *
exchange_nuclei *
bond_len_nuclei *
bond_ang_nuclei *
tors_ang_nuclei *
groups_nuclei *
******* Pulse Sequence ******************************
CHN 1
timing(usec) [10]5000
power(kHz) [0]5000
phase(deg) [0]5000
freq_offs(kHz) [0]5000
******* Variables ***********************************
******* Options *************************************
rho0 2*I1zI2z
observables 2*I1zI2z 2*I1zI3z 2*I2zI3z ....
EulerAngles *
n_gamma *
line_broaden(Hz) *
zerofill *
FFT_dimensions *
options -oes
with triangle.cor:
-2.0 0. 0. H1
0. 1.4 0. H2
1.2 0. 0. H3
and triangle.dip:
*
1 *
1 1 *
Mikhail Veshtort
I am not sure I understand your questions very well, but I'll try to
do my best to answer anyways...
First of all, there are no such things as a "liquid state mode" and a
"solid-sate mode". There is a distinction between MAS and static
"modes" though. As soon as you put an asterisk or a zero at the
spinning frequency line, it is static; a non-zero number makes it an
MAS experiment. The obvious difference between the two is that in the
former case, the anisotropic interactions are time-independent, while
in the latter case, they are modulated by the magic-angle spinning.
Second, the program does not know anything about tumbling. I am
guessing that you want to have residual dipolar couplings in your
molecule. But the dipolar couplings computed by the program
(automaticaly) from the atomic coordinates are for a molecule in a
solid. In general, if you want to put in RDC's, I think, you first
need to know what they are, and then you can put them individually as
anisotropic J-coupling tensors *instead* of providing atomic
coordinates. In the simplified case, when the molecule moves strictly
as a whole, you can probably just scale the dipolar couplings computed
from the atomic coordinates instead. I don't know much about RDC's
though, so, folks who do know these things, please correct me if I am
wrong.
Best,
Mikhail