Theoretical Variants of Bct-Si Allotropes, Composed of Rings and Cubes, Fused

New silicon allotropes, variants of bct-Si4, formed by Si4 rings, and Si8 cubes, have been derived, observing several allotropes of graphene, such as: C4 - 10I, C4 -12, and C4 - 8R1. The first two forms are composed of two and three flat, fused C4 rings: C 6 and C 8; joined to four other groups C6, in the first, and C8, in the second, allotrope variant. The C4 - 8 - R phase would be dormant by diatomic carbon chains, linked to C6 groups, formed by two fused carbon rings, C4. These sp3 three-dimensional allotropes, show variants of the bct - C 4, formed by flat rings, C 4 and cubes, C 8, independent and fused, are possible, to form new variants or allotropes Bct, of silicon, semiconductors, which could then have some application in component electronics. Its basic properties will also be studied in nonlinear optics; trying to provide a complete study on these new allotropes, variants of Bct - C4.