# Kpcs.m

Computes pseudocontact shifts using the PDE method. Computes the three-dimensional distribution of pseudocontact shift field by solving Kuprov-Charnock equation for PCS. For further information on the equations and algorithms used in this function see http://dx.doi.org/10.1039/C4CP03106G

## Syntax

    [pcs_vals,pcs_cube]=kpcs(probden,chi,ranges,nxyz,method)


## Arguments

    probden - paramagnetic centre probability density cube.

chi     - electron magnetic susceptibility tensor in cubic Angstroms.

ranges  - Cartesian axis extents for the electron spin density cube
as [xmin xmax ymin ymax zmin zmax] in angstroms.

nxyz    - nuclear coordinates as [x y z] with multiple rows) at which
PCS is to be evaluated, in Angstroms.

method  - 'fft' for Fourier transfrom solver (recommended), 'fdiff'
for a finite difference solver.


## Returns

    pcs_vals - pseudocontact shift in ppm at each nucleus.

pcs_cube - pseudocontact shift field on the same grid as the spin
density supplied.


## Examples

See the pseudocontact shift analysis tutorial and the examples in nmr_paramag directory of the standard example set supplied with Spinach.

## Notes

1. Minimal three-point schemes are used for the finite difference operators. Increase stencil size in the source code if you have enough memory.
2. Beware of the periodic boundary condition effects - leave enough space on all sides of your paramagnetic centre probability density for the wraparound PCS to become negligible.