Graphene smaller amplitude and higher frequency. This phenomenon, named "membrane effect", was predicted by Lifshitz in 1952. A prediction that was published in 2015 suggested a melting point of ≈4125 K. Recent and more sophisticated modelling has increased this temperature to at least 5000 K. At 6000 K (the sun's surface having an effective temperature of 5,777 K) graphene melts into an agglomeration of loosely coupled doubled bonded chains, before becoming a gas. The carbon–carbon bond length in graphene is about 0.142 nanometers. Graphene sheets stack to form graphite with an interplanar spacing of . Graphene is the strongest material ever
Two-electron atom Two-electron atom In atomic physics, a two-electron atom or helium-like ion is a quantum mechanical system consisting of one nucleus with a charge of "Ze" and just two electrons. This is the first case of many-electron systems where the Pauli exclusion principle plays a central role. It is an example of a three-body problem. The first few two-electron atoms are: The Schrödinger equation for any two-electron system, such as the neutral Helium atom (He, "Z" = 2), the negative Hydrogen ion (H, "Z" = 1), or the positive Lithium ion (Li, "Z" = 3) is: For a more rigorous mathematical