  Crystal structure prediction for a given chemical composition has long been a
challenge in condensed-matter science. We have recently shown that experimental
powder X-ray diffraction (XRD) data are helpful in a crystal structure search
using simulated annealing, even when they are insufficient for structure
determination by themselves (N. Tsujimoto et al., Phys. Rev. Materials 2,
053801 (2018)). In the method, the XRD data are assimilated into the simulation
by adding a penalty function to the physical potential energy, where we used a
crystallinity-type penalty function defined by the difference between
experimental and simulated diffraction angles. To improve the success rate and
noise robustness, we introduce a correlation-coefficient-type penalty function
adaptable to XRD data with significant experimental noise. We apply the new
penalty function to SiO$_2$ coesite and $\epsilon$-Zn(OH)$_2$ to determine its
effectiveness in the data assimilation method.
