聚甲基丙烯酸甲酯和聚碳酸酯各向异性光学性质理论研究

作为重要的光学薄膜材料,聚甲基丙烯酸甲酯(PMMA)和聚碳酸酯(PC)在诸多工业领域已得到广泛应用.本文利用密度泛函理论结合分子动力学方法深入系统地研究了这两种聚合物的各向异性光学性质,并对比分析了不同分子链长度和微观结构对其各向异性光学性质的影响.计算结果表明PMMA和PC都具有较高的本征双折射率,且分子链长度对本征折射率的影响显著.在可见光范围内,单体单元PMMA本征双折射率在10%以上,而三单元结构本征折射率则不到4%.对于体相结构多聚体,从立方结构拉伸到厚度仅有6?的过程中,PC不同方向折射率最大差异高达6%,而同样情况下PMMA不同方向折射率差异仅有1.3%.此项研究有助于理解PMMA和PC聚合物各向异性光学特征产生的原因和影响因素,从而进一步指导和促进其在更多领域的发展与应用.     

质子与羟基碰撞的含时密度泛函理论研究

采用将含时密度泛函理论和分子动力学非绝热耦合的方法,研究了不同入射速度下质子与羟基碰撞的反应动力学.计算了碰撞前后质子动能和羟基动能的变化及羟基电子和质子的运动.计算结果表明,质子沿垂直羟基分子轴方向入射时,质子与羟基碰撞后,质子被反弹且动能损失并俘获了羟基中氧的一部分电子,而丢失部分电子的羟基则获得动能以伸缩振动的形式向计算边界平动.随着入射质子的初动能增加,质子从羟基中俘获的电子增多,碰撞后羟基的键长变长,羟基振动变强而伸缩振动频率降低.此外,还发现质子的入射方向对碰撞过程的激发动力学有很大的影响.质子从不同的方向入射时,质子的入射初动能越大,其损失的动能越多且损失的动能与入射初动能呈线性关系,而入射方向对质子动能损失的影响很小.在质子入射初动能较低(小于25 eV)的情况下,羟基获得的动能与质子入射初动能呈线性关系且与入射方向无关;在质子入射初动能较高(大于25 eV)时,当质子沿羟基分子轴方向入射时,羟基动能的增量远大于质子沿垂直于羟基分子轴方向入射时羟基动能的增量.     

农药辛硫磷的密度泛函理论计算及拉曼光谱分析

辛硫磷(Phoxim)是一种高效、低毒、低残留有机磷杀虫剂,能抑制胆碱酯酶活性.辛硫磷的分子构型用Gauss View 5.0构造,理论计算采用密度泛函理论(density functional theory, DFT)的B3LYP/6-31+G(d, p)基组计算农药辛硫磷的拉曼光谱,实验上则采用分辨率为2 cm~(-1)的三级显微拉曼光谱检测仪对辛硫磷-甲醇溶液,辛硫磷乳油进行拉曼光谱检测.将理论拉曼光谱与实验拉曼光谱进行对比,其中有几个对应比较一致的拉曼光谱峰分别位于667, 745, 997, 1025, 1298, 1588 cm~(-1)处.首次报道了辛硫磷的拉曼光谱,同时对辛硫磷在600～1800 cm~(-1)区间的拉曼光谱进行了指认,指出了其在相应的频移位置产生较强拉曼光谱的分子振荡模式.     

一种基于密度泛函理论计算晶体结合能的变分法

提出了一种基于密度泛函理论计算晶体结合能的变分法，利用该方法初步计算了ＬｉＦ、ＮａＦ、ＫＦ、ＬｉＣｌ、ＮａＣｌ和ＫＣｌ这六种典型离子晶体的结合能、平衡晶格常数和体弹性模量，与实验结果进行了比较，分析了存在的问题，并指出了与其它同类方法相比该方法的优点     

几个小分子静电势的密度泛函理论计算

运用多种密度泛函理论(DFT)方法和从头算(ab initio)方法,研究了具有代表性的一系列分子的静电势,选择QCISD计算出的分子静电势为标准静电势,通过比较多种DFT法和QCISD从头算,以及它们之间的均方根偏差和静电势差值曲线图,结果表明B3LYP-DFT法与QCISD-ab initio法计算结果较吻合,暗示了B3LYP-DFT法在得到分子静电势时是一个有用的工具,尤其对于从头计算难以进行研究的大分子体系.     

N、P掺杂硼烯/石墨烯异质结的密度泛函理论研究

采用基于密度泛函理论的第一性原理计算方法系统研究了氮、磷掺杂对硼烯/石墨烯异质结的几何结构和电子性质的影响.结果表明,相较完整硼烯/石墨烯异质结的金属特性,氮、磷掺杂的硼烯/石墨烯异质结均表现为半导体特性.室温下的分子动力学模拟进一步论证了相关体系的动力学稳定性.研究结果能够为硼烯/石墨烯异质结在新型二维半导体材料中的应用提供参考价值.     

δ-Pu空位缺陷的密度泛函理论计算

采用密度泛函理论框架下的平面波赝势方法,计算了空位缺陷对δ-Pu结构稳定性和电子结构的影响.建立了1×1×2、2×2×1和2×2×2 3种晶胞中的空位缺陷模型,分别计算了其晶格常数、空位形成能、结合能、态密度、电荷密度分布以及Mulliken电荷布居.计算结果表明:空位缺陷在δ-Pu中不能稳定存在,且会导致晶体的整体结构稳定性降低.在3种缺陷模型中,2×2×1的模型空位稳定性和结构稳定性都相对更强;空位导致δ-Pu电子的局域性降低,电子相互作用也发生了一定的变化,其中2×2×1的模型中与空位最邻近的Pu原子发生了明显的sp杂化,这在一定程度上说明了其稳定性最强的原因;空位引起电荷由近空位端向近Pu端转移,且导致最邻近Pu原子失去电子,而这部分电子主要由6p轨道贡献.     

密度泛函理论的若干进步

密度泛函理论（ＤＦＴ）作为处理非均匀相互作用多粒子体系的近似方法已经在计算凝聚态物理、计算材料科学和计算量子化学诸多领域取得巨大成功并获得广泛应用。然而它也存在一些被广泛关注的弱点或困难。例如关于激发态问题,强关联问题和处理大原子数复杂体系方面的困难。本将针对ＤＦＴ在以上三方面的问题,评述近年来的主要努力和进展。着重量介绍最近发展的含时间密度泛函理论（ＴＤＦＴ）,它有可能发展成为处理激发态问题的标准方法。关于强电子关联体系的处理,主要介绍ＬＤＡ以外的新发展,包括ＬＤＡ＋＋方法和计及动力学平均场理论的ＬＤＡ＋ＤＭＦＴ方法。最后,评述ＤＦＴ框架内的线性标度Ｏｒｄｅｒ－Ｎ算法的物理基础和主要策略。该算法将在处理大原子数复杂体系问题上发挥重要作用。     

四碘甲状腺素团簇结构与光谱性质的密度泛函理论研究

在B3LYP/Lanl2mb基组水平上,利用密度泛函理论(DFT)优化了四碘甲状腺素团簇的几何结构.基于该团簇的几何结构下,其吸收和发射光谱的研究使用相同的基组水平并采用极化连续介质模型(PCM)下用含时密度泛函理论(TDDFT).研究结果表明,优化所得甲状腺素团簇的几何结构对称性为C_1;在基态稳定结构基础上,得出其输运性质,即甲状腺素团簇为p型输运材料;通过含时密度泛函理论,在优化好的基态结构基础上,又计算了它的溶剂效应,进一步得出该分子在水溶剂中的吸收光谱和发射光谱特性.     

三碘甲状腺素团簇结构与光谱性质的密度泛函理论研究

我们利用密度泛函理论(DFT),在B3LYP/Lan12mb基组水平上,得到了三碘甲状腺素团簇的几何和电子结构.在此基础上,利用含时密度泛函理论(TDDFT),使用相同的基组和采用极化连续介质模型(PCM),对其溶剂效应下的吸收光谱进行研究．研究结果表明,优化所得三碘甲状腺素团簇的对称性为C₁;在基态稳定结构基础上,研究了该分子的红外和拉曼分子振动谱特性,同时研究了其输运性质,即三碘甲状腺素团簇为p型输运材料;通过含时密度泛函理论,在优化好的基态结构基础上,又计算了它的溶剂效应,进一步得出该分子在水溶剂中的吸收光谱特性.     

Vibrational analysis of L-serine using the density functional theory

In this paper, we present a computational study of L-serine using ab initio molecular dynamics simulation based on density functional theory (DFT) within the ultrasoft pseudopotentials and generalized-gradient approximation. Taking into account the intermolecular interactions, we can indeed simulate the features of the experimental results very well for L-serine zwitterions in its solid state. The vibrational spectrum of L-serine performed by DFT was in excellent agreement with our previous inelastic incoherent neutron scattering spectra measured at 20K for L-serine in the 10--200meV region on HET spectrometers at ISIS, Rutherford Appleton Laboratory.     

Investigation of the dissociative adsorption for cyclopropane on the copper surface by density functional theory and quantum chemical molecular dynamics method

The dissociative adsorption of cyclopropane on the copper surface was studied using quantum chemical molecular dynamics method with “Colors-Excite” code and density functional theory by Amsterdam Density Functional program (ADF2000). The excited state of cyclopropane was used as adsorbate to simulate the dissociated adsorption under an irradiation energy of ca. 10 eV. One of the C-C bonds in cyclopropane was broken and the two new bonds between cyclopropane and copper surface were formed. The electrons transferred from the copper atoms to cyclopropane with a value of about 0.2e. The shorter distances between the carbons and surface copper atoms showed the existence of strong interaction. Consistently, the results indicated metallacyclopentane was the most possible intermediate species in dissociative adsorption by ADF2000 and “Colors-Excite” method.     

Ionic solvation and association in LiCl aqueous solution: a density functional theory,polarised continuum model and molecular dynamics investigation

In this work, the ionic solvation and association behaviours in the LiCl aqueous solution were investigated using density functional theory (DFT), a polarised continuum model and classical molecular dynamics simulations. DFT calculations of LiCl(H₂O)_1–6,8 clusters show that contact ion pair (CIP) and solvent-shared ion pair (SSIP) conformers of LiCl(H₂O)_n (n ≥ 4) clusters are generally energetic both in the gas phase and in the aqueous solution. Some SSIP conformers may be slightly more stable than their CIP isomers when at least eight water molecules are incorporated in the inner hydration shells of LiCl hydrates. The transformation between CIP and SSIP conformers is easy by overcoming a small energy barrier, which mainly results from the hydration shell reorganisation of Li⁺. Molecular dynamics simulations show that ion pairs or ion clusters can be found in the LiCl aqueous solution, and the probability of CIP conformers or ion clusters presented in the LiCl solution generally increases with rise in temperature. However, the presentation of ion pairs or ion clusters in the LiCl aqueous solution does not inevitably lead to the nucleation of LiCl crystallisation.     

Wave packet molecular dynamics–density functional theory method for non‐ideal plasma and warm dense matter simulations

A new wave packet molecular dynamics–density functional theory (WPMD‐DFT) method is proposed for atomistic simulations of non‐ideal plasma and warm dense matter. The method is based on the WPMD approach, where the electronic exchange and correlation effects are treated using an additional energy term taken from DFT. This term is calculated by integration over the mesh values of the wave packet density. The local density approximation is implemented so far. WPMD‐DFT is meant as a replacement for the anti‐symmetrized WPMD (AWPMD) method which is more time consuming and lacks electron correlation. In this paper, we compare the results obtained by WPMD‐DFT, WPMD, AWPMD, classical molecular dynamics, and path integral Monte Carlo methods for the internal energy of the hydrogen plasma in the temperature range 10–50 kK and electron number density from 10²⁰ to 10²⁴ cm^?3. We also demonstrate the ability to handle the simultaneous dynamics of electrons and ions by calculating the electron–ion temperature relaxation. The scalability of the WPMD‐DFT method with the number of electrons is shown for implementations in central processing unit and graphical processing unit.     

Electron dynamics triggered by double attosecond pulses: Simulations based on time-dependent density functional theory

In order to observe the high-field effect, the external laser field must reach its peak intensity before the electron ionization. To this end, it is important to reduce pulse duration to typical attosecond timescale. In this paper, the interaction electron dynamics between attosecond pulses and dielectric is investigated within the time-dependent density functional theory. Taking the CaF₂ crystal as an example, we give a comparison of electron dynamics response between single and double pulses. Moreover, the nonlinear energy absorption and electron excitation processes are simulated by adjusting the polarization direction of the sub-pulse. Present results demonstrate that the double pulses show lower electron excitation and energy absorption than the single pulse, which is in accordance with experimental higher ablation threshold and smaller heat-affected zones of the double pulses. In addition, the curves of final excited electron number and energy absorption exhibit the quasi-symmetry about the axis of 180°, which has not been reported yet.     

Hydration characteristics of Ca2+ and Mg2+: a density functional theory,polarized continuum model and molecular dynamics investigation

In this work, density functional theory, Møller–Plesset second-order perturbation theory, and ab initio molecular dynamics (AIMD) were used to investigate hydrated characteristics of Mg²⁺ and Ca²⁺ as a function of coordination number in the first hydration shell (CN) and cluster size. It is generally accepted that the CNs of Mg²⁺ and Ca²⁺ are both six. Calculations show that the hydration of Mg²⁺ generally prefers six-coordinated structures, whereas the CN value of Ca²⁺ varies from 6 to 8 as the hydration proceeds. Moreover, the first hydration of Ca²⁺ is found to be more flexible than that of Mg²⁺, as indicated by the results of transition state calculations and AIMD simulations. In addition, the constraint of Mg²⁺ on the first hydration shell is obviously stronger than that of Ca²⁺, while the constraint on the inner hydration shells fades slightly faster for Mg²⁺ than Ca²⁺. It is also found that the charge transfer from central cation to water molecules is affected only by the first hydration shell for Mg²⁺, whereas by the first and second hydration shells for Ca²⁺. Based on hydration characteristics, approximatively saturated ion hydration shells for the hydration of Mg²⁺ and Ca²⁺ were proposed.     

Universality principle and the development of classical density functional theory

The universality principle of the free energy density functional and the ‘test particle' trick by Percus are combined to construct the approximate free energy density functional or its functional derivative. Information about the bulk fluid radial distribution function is integrated into the density functional approximation directly for the first time in the present methodology. The physical foundation of the present methodology also applies to the quantum density functional theory.     

碳分子线C5在激光场中的含时密度泛函理论研究

运用含时密度泛函理论和分子动力学相结合的方法, 研究了C₅分子线在强激光场中的电离激发.研究发现, 当考虑激光强度对C₅分子线激发的影响时, 激光强度越强, 分子吸收的能量越多, 电离也越早, 最终电离的电子也越多, 而且沿激光极化方向的偶极矩的变化及峰值也越大. 关于激光极化方向对C₅分子线激发的影响的研究表明, 当激光极化方向沿着C₅分子线轴向时, 分子的电离大大增强, x方向的激光脉冲仅能激发起x方向的偶极振荡, 而y方向的激光脉冲仅能激发起y方向的偶极振荡, 而且x方向的激光脉冲激发的偶极振荡强. 研究还表明, 当激光极化方向沿着C₅分子线轴向时, 尽管由于电离增强而导致C₅分子线C–C键振动的同步性变差, 但在两种激光极化方向情况下, C₅分子线的振动模式与中性C₅分子线的振动模式相同. 关键词： 含时密度泛函理论 分子动力学 分子电离 碳分子线