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We have modeled the transformation of cellulose Iβ to a high temperature (550 K) structure, which is considered to be the first step in cellulose pyrolysis. We have performed molecular dynamics simulations at constant pressure using the GROMOS 45a4 united atom forcefield. To test the forcefield, we computed the density, thermal expansion coefficient, total dipole moment, and dielectric constant of cellulose Iβ, finding broad agreement with experimental results. We computed infrared (IR) spectra of cellulose Iβ over the range 300–550 K as a probe of hydrogen bonding. Computed IR spectra were found to agree semi-quantitatively with experiment, especially in the O–H stretching region. We assigned O–H stretches using a novel synthesis of normal mode analysis and power spectrum methods. Simulated IR spectra at elevated temperatures suggest a structural transformation above 450 K, a result in agreement …