  The conventional method of generating initial conditions for cosmological
N-body simulations introduces a significant error in the real-space statistical
properties of the particles. More specifically, the finite box size leads to a
significant underestimate of sigma_8, the correlation function, and nonlinear
effects. I implement a method of generating initial conditions for N-body
simulations that accurately models the real-space statistical properties, such
as the mass variance in spheres and the correlation function. The method
requires running ensembles of simulations because the power in the DC mode is
no longer assumed to be zero. For moderately sized boxes, I demonstrate that
the new method corrects the underestimate in the mass variance in spheres and
the shape of the correlation function. I also argue that subtracting Poisson
noise from the power spectrum is a dangerous practice. Code to generate initial
conditions to second order in Lagrangian perturbation theory with the new
method is available at http://www.astro.princeton.edu/~esirko/ic .
