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Anisotropy and temperature dependence of structural, thermodynamic and elastic properties of crystalline cellulose I β were computed with first-principles density functional theory (DFT) and a semi-empirical correction for van der Waals interactions. Specifically, we report the computed temperature variation (up to 500 K) of the monoclinic cellulose I β lattice parameters, constant pressure heat capacity, C p , entropy, S, enthalpy, H , the linear thermal expansion components, ξ i , and components of the isentropic and isothermal (single crystal) elastic stiffness matrices, C S ij (T ) and C T ij (T ), respectively. Thermodynamic quantities from phonon calculations computed with DFT and the supercell method provided necessary inputs to compute the temperature dependence of cellulose I β properties via the quasi-harmonic approach. The notable exceptions were the thermal conductivity components, λ i (the prediction of which has proven to be problematic for insulators using DFT) for which the reverse, non-equilibrium molecular dynamics approach with a force field was applied. The extent to which anisotropy of Young's modulus and Poisson's ratio is temperature-dependent was explored in terms of the variations of each

a b s t r a c tMolecular dynamics simulation is commonly used to study the properties of nanocellulose-based materials at the atomic scale. It is well known that the accuracy of these simulations strongly depends on the force field that describes energetic interactions. However, since there is no force field developed specifically for cellulose, researchers utilize models parameterized for other materials. In this work, we evaluate three reactive force field (ReaxFF) parameter sets and compare them with two commonly-used non-reactive force fields (COMPASS and GLYCAM) in terms of their ability to predict lattice parameters, elastic constants, coefficients of thermal expansion, and the anisotropy of cellulose I b . We find that none is able to accurately predict these properties. However, for future studies focused on a given property, this paper presents the information needed to identify the force field that will yield the most accurate results.

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