Period 2 element two make up all natural occurrence of lithium on Earth, although further isotopes have been synthesized. In ionic compounds, lithium loses an electron to become positively charged, forming the cation Li. Lithium is the first alkali metal in the periodic table, and the first metal of any kind in the periodic table. At standard temperature and pressure, lithium is a soft, silver-white, highly reactive metal. With a density of 0.564 g·cm, lithium is the lightest metal and the least dense solid element. Lithium is one of the few elements synthesized in the Big Bang, making it a primordial element. Lithium
Helical boundary conditions Helical boundary conditions In mathematics, helical boundary conditions are a variation on periodic boundary conditions. Helical boundary conditions provide a method for determining the index of a lattice site's neighbours when each lattice site is indexed by just a single coordinate. On a lattice of dimension "d" where the lattice sites are numbered from 1 to "N" and "L" is the width (i.e. number of elements per row) of the lattice in all but the last dimension, the neighbors of site "i" are: It is not necessary that "N" = "L". Helical boundary conditions make it possible to use only