Improving initial conditions for cosmological N-body simulations

Lehman H. Garrison, Daniel J. Eisenstein, Douglas Ferrer, Marc V. Metchnik, Philip A. Pinto

Research output: Contribution to journalArticlepeer-review

53 Scopus citations


In cosmological N-body simulations, the representation of dark matter as discrete 'macroparticles' suppresses the growth of structure, such that simulations no longer reproduce linear theory on small scales near kNyquist. Marcos et al. demonstrate that this is due to sparse sampling of modes near kNyquist and that the often-assumed continuum growing modes are not proper growing modes of the particle system. We develop initial conditions (ICs) that respect the particle linear theory growing modes and then rescale the mode amplitudes to account for growth suppression. These ICs also allow us to take advantage of our very accurate N-body code ABACUS to implement second-order Lagrangian perturbation theory (2LPT) in configuration space. The combination of 2LPT and rescaling improves the accuracy of the late-time power spectra, halo mass functions, and halo clustering. In particular, we achieve 1 per cent accuracy in the power spectrum down to kNyquist, versus kNyquist/4 without rescaling or kNyquist/13 without 2LPT, relative to an oversampled reference simulation.We anticipate that our 2LPT will be useful for large simulations where fast Fourier transforms are expensive and that rescaling will be useful for suites of medium-resolution simulations used in cosmic emulators and galaxy survey mock catalogues. Code to generate ICs is available at

Original languageEnglish (US)
Pages (from-to)4125-4145
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Oct 1 2016


  • Galaxies: haloes
  • Large-scale structure of Universe
  • Methods: numerical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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