UPDATED 8/19/2020
NOTICE TO READERS: This article has been removed because the original manuscript from the researchers was retracted due to calculational errors in the mechanical properties of pentadiamond. The researchers released the following statement about their work:
Based on feedback from several groups (see below), we carefully rechecked the mechanical properties and found serious mistakes in the optimized structure of pentadiamond under mechanical deformation. Our new calculations reveal that pentadiamond is not a hard material and has a positive Poisson ratio. For your convenience, we list newly obtained data: 1. Elastic constants are c11=645 GPa, c12=88 GPa, and c44=194 GPa. 2. Bulk modulus =274 GPa, averaged Young’s modulus =522 GPa, averaged shear modulus =220 GPa, and averaged Poisson ratio =0.18.
We regret these errors, which were caused by the total energy calculations of pentadiamond with an inappropriate choice of structural deformation. We thank S. Saha, W. von der Linden, L. Boeri, P. B. Howes, V. V. Brazhkin, M. V. Kondrin, A. G. Kvashnin, E. Mazhnik, A. R. Oganov, Davide M. Proserpio, Chaoyu He, and Volker L. Deringer for pointing out our errors.