  The abundance of glycine (Gly), the simplest amino acid, in meteorites leads
us to the next question about its extraterrestrial origin. However, astronomers
have not yet found glycine signature in interstellar medium. Laboratory
microwave spectroscopy experiments report the most stable Gly conformer has a
dipole moment of 4.5 - 5.45 Debye. Theoretical calculations, so far performed
only with Gaussian basis functions, has predicted a dipole moment of about 1
Debye. This discrepancy has baffled astronomers. We study the energetics of
glycine and its isomers and conformers via plane-wave density functional theory
calculations. The geometric structures of the isomers and their conformers are
identified, along with their relative stability and their dipole moment. In the
case of glycine, we obtain the most stable conformer with a dipole moment of
5.76 Debye, close to the microwave spectroscopy experiments. If the plane wave
energy cutoff is reduced to a lower value (~400 eV) on purpose, the energy
ordering reverses to the case with Gaussian basis calculations.
