气相甘氨酸的新能量有序和偶极矩的平面波密度泛函理论计算
A New Energy Ordering of Gas Phase Glycine and the Dipole Moment via Plane-wave Density Functional Theory Calculations
摘要：
甘氨酸（Gly），最简单的氨基酸，在陨石中的丰富，使我们对它的外星起源的下一个问题。然而，天文学家尚未在星际介质中发现甘氨酸签名。实验室微波光谱实验报告最稳定的甘氨酸构象具有4.5 - 5.45德拜的偶极矩。理论计算，迄今为止只进行高斯基函数，预测偶极矩约为1德拜。这种差异令天文学家感到困惑。我们通过平面波密度泛函理论计算研究了甘氨酸及其异构体和构象的能量学。确定了异构体及其构象的几何结构，以及它们的相对稳定性和它们的偶极矩。在甘氨酸的情况下，我们得到了最稳定的构象与5.76德拜的偶极矩，接近微波光谱实验。如果故意将平面波能量截止降低到较低值（~400 eV），则能量排序与高斯基计算的情况相反。
英文摘要：
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.
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