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تسجيل مستخدم جديدComment on Pentadiamond: A Hard Carbon Allotrope of a Pentagonal Network of sp2 and sp3 atoms
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In a recent Letter [1] Y. Fujii et al. proposed a new carbon allotrope and claimed its extremely high Youngs and shear moduli of 1691 and 1113 GPa, respectively, surpassing those of diamond by 1.5 and 2 times! The authors also claimed unique negative averaged Poissons ratio of -0.24, bulk modulus of 381 GPa and record value of the sound speed 28.7 km/s for this carbon modification. Here we show by two independent computations that these values were obtained as a result of errors. The new hypothetical allotrope has in fact quite moderate elastic moduli, unremarkable for a carbon structure with similar density: bulk modulus of 250 GPa, shear modulus of 170 GPa,Youngs modulus of 417 GPa, positive Poissons ratio of 0.22.
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