Maling N, Lempka SF, Blumenfeld Z, Bronte-Stewart H, McIntyre CC (2018) Biophysical basis of subthalamic local field potentials recorded from deep brain stimulation electrodes. J Neurophysiol 120:1932-1944
doi: 10.1152/jn.00067.2018

have made the NEURON simulator code available at their github repository:

https://github.com/Nickmaling/STN_LFP_Model