# Is basis set superposition error reduced when using the GAPW method?

CP2K implements the Gaussian and Augmented Planewaves (GAPW) approach for all-electron calculations. My understanding is that the GAPW method involves using atom-centered Gaussian type orbitals to represent rapidly varying electron density around nuclei, and planewaves for the electron density in the slowly varying interstitial regions.

My question is: does use of the GAPW method mostly eliminate basis set superposition error effects, for example bond length contraction during optimization? I would think so, since the core regions probably will not overlap in most systems, but I may be misunderstanding how GAPW works.

• +1, would be good to know but this definitely gave some confusion as I thought this referred to GPAW at first. Dec 16, 2020 at 22:25
• @TristanMaxson That was my fault since I added the GPAW tag. There's space for 2 more tags, which would help the user's question get seen by more people, and in more chat rooms, such as this one: chat.stackexchange.com/rooms/112878/gpaw. Does the question have to be about GPAW to have that tag? AW and PAW and APW questions that weren't specifically about GPAW, have used that tag before, and other software tags have been used when it was believed that members of those programs' communities might be able to help. Maybe we can discuss here chat.stackexchange.com/rooms/107328/tags? Dec 16, 2020 at 23:28

I would also like to point out here that if one is pursuing periodic calculations with Gaussian basis sets, the basis functions are not really Gaussian anymore since one is actually using Bloch functions $$\chi_\mu ({\bf k};{\bf r}) = \sum_{\bf g} \chi_\mu ({\bf r}-{\bf g}) \exp(i {\bf k} \cdot {\bf r})$$, see e.g. the book by Pisani, Dovesi, and Roetti, doi:10.1007/978-3-642-93385-1.