# Masdnp.m

Magic angle spinning DNP simulation.

## Syntax

    dnp=masdnp(spin_system,parameters)


## Description

The function returns the rotor period averaged steady state magnetization. The implementation takes a lot of inspiration from the code donated by Frederic Mentink-Vigier, please cite Fred's papers (http://dx.doi.org/10.1016/j.jmr.2015.07.001 and http://dx.doi.org/10.1016/j.jmr.2012.08.013) if you are using it.

## Arguments

    parameters.spins    -  a cell array of strings listing the spins to
which the parameters.offset variable refers

parameters.rate     -  spinning rate, Hz

parameters.axis     -  spinning axis direction vector.

parameters.max_rank -  rotor discretization grid rank, typically in the thousands

parameters.mw_pwr   -  microwave power, Hz

parameters.mw_frq   -  microwave frequency, Hz

parameters.eq_time  -  equilibration time, seconds

parameters.grid     -  the name of the spherical averaging grid

parameters.coil     -  detection state

parameters.verbose  -  set this to 1 to enable diagnostic output


## Returns

The function returns the steady state population of the detection state.

## Examples

A detailed walkthough for solid effect and cross effect MAS DNP is given in the example set. For a simple three-spin system discussed in Fred's paper, cross_effect_mas_enlev.m returns the rotor phase dependence of the energy levels in the system:

The energy level population dynamics during the first rotor cycle is returned by cross_effect_mas_dynam.m example:

The energy level population dynamics during the steady state rotor cycle is returned by cross_effect_mas_steady.m example:

and finally the steady state rotor-averaged, powder-averaged DNP amplitude is returned by a call to this function in cross_effect_mas_powder.m example file.

## Notes

1. The steep transitions visible in the figures above necessitate very large rotor grids, typically thousands of points. Our attempts at reducing this number have not been successful.
2. Because DNP simulations involve strong anisotropic interactions acting for a long time, large powder averaging grids are likely to be needed. Always check that your calculation is converged with respect to the size of the spherical grid.