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TuningSpeedMem

This page gives hints on how to tune the speed and memory usage with the ABINIT package.

Introduction

The major factors governing the speed of an ABINIT run, for a given physical system, are:

For the two first factors, there is a trade-off between CPU time and precision of the computation, while for the third factor, there is some limit on the maximal speed-up that can be achieved (and also, the resources must be available.

Beyond these major factors, there is still room for some adjustment. The needed planewave basis set will depend on the pseudopotential (or PAW atomic dataset) that is used. Some might be softer than others and need a smaller planewave basis set. They might possibly be less accurate as well …

If one is only interested in ground-state properties and forces, one might also get some speed up by using a real-space representation of density and potential on a real space FFT grid that does not allow their fine details to be taken into account (actually, filtering such quantities). This is achieved by lowering boxcutmin below its theoretically needed value of 2.0.

The choice of the FFT algorithm implementation, see fftalg might also lead to significant speed up, on specific machines.

For specific k-points, time-reversal symmetry can be used to represent the wavefunctions with their real part, instead of both their real and complex parts. This allows halving the memory needs, as well as the CPU time. See istwfk.

GW calculations can be made less memory and CPU time consuming, at the expense of numerical precision, by compiling ABINIT with the option enable_gw_dpc=“no” in the *.ac9 file.

Aside of using input variables, sometimes, to solve memory problems, the user has to increase the stack size limit. using Linux/Osx, one can get the stack size using “ulimit -s”, and set it to a larger limit using e.g. “ulimit -s 16384” for 16MB cache size, or “ulimit -s unlimited” if the OS allows you to do so. Note that in version 9.4.1, this operation is automatically performed by Abinit at the beginning of the run.

Other input variables related to tuning the speed or the memory usage are for expert users only.

basic:

  • boxcutmin BOX CUT-off MINimum
  • istwfk Integer for choice of STorage of WaveFunction at each k point

useful:

  • fftalg Fast Fourier Transform ALGorithm
  • mixprec MIXed PRECision
  • rmm_diis Activate the RMM-DIIS eigensolver for GS calculations.
  • rmm_diis_savemem Save memory in the RMM-DIIS eigensolver.

expert:

  • exchn2n3d EXCHange N2 and N3 Dimensions
  • extrapwf flag - EXTRAPolation of the Wave-Functions
  • fftcache Fast Fourier Transform CACHE size
  • gwmem GW MEMory
  • iboxcut Integer governing the internal use of BOXCUT - not a very good choice of variable name
  • nbdblock Number of BanDs in a BLOCK
  • nloc_alg Non LOCal ALGorithm
  • nloc_mem Non LOCal MEMOry
  • ortalg ORThogonalisation ALGorithm
  • useylm USE YLM (the spherical harmonics)

Selected Input Files

v3: