deletions | additions       diff --git a/Photoemission.tex b/Photoemission.tex  index ff7453b..7b7e817 100644  --- a/Photoemission.tex  +++ b/Photoemission.tex 
...
This cost can be greatly reduced using a special grid with only two additional points placed at $\pm \alpha L$   as shown in Fig.~\ref{fig:pes_nfft}~(c).  Since the new grid has non uniform spacing a non-equispaced FFT (NFFT) must be   employed~\cite{Kunis:2006wg,Potts:2009kn}. is used~\cite{Kunis:2006wg,Potts:2009kn}.  With this strategy a price is paid in momentum space where the maximum momentum $k_{\rm max}$ is reduced   by a factor $\alpha$ compared to ordinary FFT.  In Octopus we implemented all the three strategies: bare FFT, zero padding with FFT and zero padding with NFFT.