NaBH₄的第一原理计算及SrOD分子的电子结构研究

【作者】 左坤；

【导师】 杨战营；

【作者基本信息】 西北大学 ， 物理学， 2010， 硕士

【摘要】 本论文的主要工作有两个：1对NaBH4的晶格结构、电子结构、弹性性质进行了计算并比较了两种近似对物性预测的效果；2 SrOD分子的电子结构研究。第一章介绍了氢及氢能、储氢原理和储氢材料的研究现状。氢能源作为一种清洁,储量丰富,利用率高的清洁能源引起了广泛的关注。在氢能的利用环节中储氢目前最为关键也是至今没有得到很好解决的一个瓶颈。目前储氢方式主要有：(1)气态储氢；(2)液态储氢；(3)纳米材料储氢；(4)金属氢化物；(5)配位金属氢化物。传统的气态,液态储氢方式由于不安全等因素制约了氢能的储存与运输。而固体储氢材料作为一种安全,运输方便,储氢密度高的储氢方式得到了广泛的研究。第二章主要介绍了近似密度函数：局域密度近似(LDA)和广义梯度近似(GGA)。由于LDA是建立在理想的均匀电子气模型基础上,而实际原子和分子体系的电子密度远非均匀的。要进一步提高计算精度,就需要考虑电子密度的非均匀性,所以就得到了GGA。第三章介绍了基于密度泛函理论的方法,采用交换关联函数的广义梯度近似(GGA)和局域密度近似(LDA)对NaBH4的晶格结构、电子结构、弹性性质进行了计算并比较了两种近似对物性预测的效果。计算表明GGA在晶格常数,能隙,弹性性质上要比LDA更准确。第四章用高斯程序优化了SrOD分子的基态键长。使用molcas程序Caspt2(全活性空间的二阶微扰)方法计算了SrOD分子的键长、键角和相对基态的能量,画出了势能曲线。在计算中,我们发现了试验上没有给出的新态2△,并得到了它的键长和能量。此外,计算确认了C2Π态是非线性结构,印证了实验上关于这个态的猜想。更多还原

【Abstract】 This paper is consist of two parts:calculations of the structural, electronic and elastic properties of NaBH4 using GGA and LDA of exchange-correlation function, comparison of the two approximation for predicting the physical properties, electronic structure research on SrOD molecular.The first chapter is consist of hydrogen, hydrogen storage principle and the situation of the research. As a kind of clean, abundant, high efficient energy carrier, hydrogen has attracted wide concern. In the process of the using of hydrogen, hydrogen storage is the most important part and has yet solved successfully. Methods for hydrogen storage are mainly:(1) gaseous storage, (2) liquid storage, (3) adsorption of nanomaterials, (4) metal hydrides, (5) complex hydride. The traditional gas, liquid storage are not ideal because of the unsafety, difficulties in hydrogen storage and transportation. While solid hydrogen storage materials have been widely studied as one kind of safe, convenient for transportation, high density of hydrogen method.The second chapter mainly introduces the approximate density function:Local density approximation (LDA)and Generalized gradient approximation(GGA). Because LDA is based on the ideal uniform electron gas model,electron density of real atoms and molecules in the system is far from uniform. In order to improve the calculation accuracy further, we need to consider the inhomogeneity of electron density. So we got GGA.In the third chapter, we calculated the lattice, electronic and elastic properties of NaBH4 based on density function theory with GGA and LDA of exchange-correlation function. Our results indicate that GGA is more favorable than LDA for predicting physical properties, such as lattice constants, band gaps and elastic properties.In the fourth chapter, we showed the methods we used to optimize SrOD molecular ground-state bond length using Gaussian code. Furthermore, Molcas program based on the MCSCF using reference state Caspt2 (the second perturbation of active space) are used to calculate the bond length, relative ground-state energy and the potential energy curve (PEC) of SrOD molecules. In conclusions, we found a new state of SrOD, which is not reported by experiments yet and calculated its bond length and PEC. We prove the configuration of C2(?) is nonlinear structure and confirm the conjecture of the experiment.更多还原