The kesterite, Cu2ZnSnS4has a big potential as a future solar material in replacing current material. Although the kesterite and copper indium gallium selenide, CIGS has almost same structure but the constituent elements of kesterite are earth-abundance, cheaper and non-toxic. The chalcogen elements existed inside the kesterite compound are selenium and sulphur, Cu2ZnSnSe4/ Cu2ZnSnS4. Therefore, the structural flexibility of kesterite opens up an avenue to develop light-absorber material with suitable properties and applications. The density functional theory (DFT) has been used to calculate the total energy of Kesterite developed from Material Studio - CASTEP. The general gradient approximation (GGA) has been choosing to treat the exchange-correlation. The structure of kesterite has been developed by determining its space group, I4 and Pc and its coordination of each atom. The previous calculated shown that the energy of its band gap is around 1.0-1.5 eV.

We have calculated the vibrational frequencies of chlorophyll-a, chlorophyll-a + 1 NaCl and chlorophyll-a + 2 NaCl from the first principle. We are able to find the vibrational frequencies as well as the structural parameters in all of the three cases. The Mg atoms are found to absorb Na atoms which distort the structure. The vibrational frequencies calculated for the chlorophyll-a are in reasonable agreement with those found from the Raman Spectra.