Ab initio predictions of the structural, spectroscopic, and energetic properties of some chemical systems

利用從頭計演算法對一些化學體系的結構, 光譜和能量等性質的研究及預測

Student thesis: Doctoral Thesis

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  • Yi PAN


Awarding Institution
Award date15 Jul 2015


In first part of this thesis, the thermochemical properties of CoC/CoC+, VN/VN+, VC/VC+, NbC/NbC+, TiO/TiO+, and TiO2/TiO2+ have been evaluated by using the wavefunction-based ab initio coupled cluster theory with single, double, triple, and quadruple excitations (CCSDTQ) and complete basis set (CBS) approach. The CCSDTQ/CBS calculations presented in this part involve the approximation to the CBS limit at the coupled cluster level up to full quadruple excitations with the zero-point vibrational energy corrections (ZPVE), the spin-orbit coupling corrections (SO), the core-valence electronic correction (CV, up to CCSDT level), the high-order corrections (HOC, up to CCSDTQ level), and the scalar relativistic effect corrections (SR, up to CCSDTQ level). Comparisons between the CCSDTQ/CBS predicted ionization energies (IEs) and the precise experimental values suggest that the CCSDTQ/CBS procedure is capable of predicting reliable IEs in chemical accuracy (less than 40 meV). Besides the theoretical predictions on IEs, the bond dissociation energy (D0) and heats of formation ∆H°f0 and ∆H°f298 of CoC/CoC+, VN/VN+, VC/VC+, NbC/NbC+, TiO/TiO+, and TiO2/TiO2+ are also presented. The second part is to study the reaction mechanism of : (i) C−N bond cleavage of anilines by a (salen)ruthenium(VI) nitrido complex; (ii) highly efficient alkane oxidation catalyzed by [MnV(N)(CN)4]2-; (iii) C−H bond activation of 9, 10-dihydroanthracene (DHA) by BF3-activated manganese(V) nitrido complex, using density functional theory (DFT). The DFT results together with the experimental determinations provide important insights into the reaction mechanism of the above reactions and suggest the transition metal complexes to be potential catalysts. In the third part, the single photon ionization process of gas phase 3-hydroxyisoquinoline (3HQ), 2-quinolinol (2Q), and thymine (T) are theoretically studied by coupled cluster and multi-reference methods. The adiabatic ionization energies of 3HQ, 2Q, and T are determined by explicitly correlated computation at CCSD(T)-F12 level with CV, SR, and ZPVE corrections. The complete active-space self-consistent field (CASSCF) and the internally contracted multi-reference configuration interaction (MRCI) approaches have been employed to predict the energetics of excited states and their vibrational spectra. The slow photoelectron spectrum (SPES) of 3HQ, 2Q, and T are assigned based on the equilibrium geometries, electronic states patterns, and anharmonic vibrational frequencies. The last part presents an efficient and novel theoretical implementation for solving the Schrödinger equation of two-dimensional torsional motions. With using current implementation, the computational time in solving Schrödinger equation for torsional energy and wavefunction is greatly reduced down to scale of seconds. The theoretical implementation has been verified on the dual methyl interactions of acetone and its cation and also applied to cis-/trans-2-butene and their cations. Comparisons between the predicted torsional frequencies and the experimental values suggest that the current theoretical implementation is fast, efficient, and reliable to predict the torsional energy levels and thus the transition frequencies. 本論文的第一部分討論使用耦合簇理論結合完全基組的方法(CCSDTQ/CBS)來預測一些雙原子分子體系(CoC/CoC+, VN/VN+, VC/VC+, NbC/NbC+, TiO/TiO+)以及三原子分子體系(TiO2/TiO2+)的熱化學性質。CCSDTQ/CBS計算是對耦合簇理論進行一至四級激發校正並外推至完全基組極限的高精度方法。其還包括了如下校正: 零點振動能校正(ZPVE),自旋耦合校正(SO),核-價電子校正(CV,至CCSDT水準),以及相對論校正(SR,至CCSDTQ水準)。由CCSDTQ/CBS方法預測的分子電離能與高準確度實驗資料相比,誤差在化學精度以內(即小於40 meV)。同時,CCSDTQ/CBS計算也給出了上述雙原子及三原子分子體系的鍵解離能(D0)和生成熱(ΔH°f0/ΔH°f298)的預測。論文的第二部分主要利用密度泛函理論(DFT)對如下一些化學反應進行機理研究:(一)使用六價釕salen氮化物對苯胺上的碳氧鍵進行活化;(二)使用五價錳氮化物([MnV(N)(CN)4]2−)對烷烴進行高效催化氧化;(三)使用被三氟化硼活化的五價錳salen氮化物對9, 10-雙氫蒽(DHA)的碳氧鍵進行活化。DFT反應機理很好地吻合了實驗結果並且肯定了上述過渡金屬化合物的催化性質。在論文的第三部分主要是用耦合簇理論以及多參考態方法對氣相的3-羥基異喹啉(3HQ),2-喹啉(2Q)以及胸腺嘧啶(T)的單光子電離過程進行理論研究。CCSD(T)-F12顯式相關計算經校正後(包括CV, SR及ZPVE校正)精確地預測了3HQ, 2Q以及T的絕熱電離能。同時,我們使用了完全活化空間自洽場(CASSCF)理論及內收縮多參考態組態相互作用(MRCI)方法預測了相關激發態的能量及光譜性質。根據計算結果,我們劃分了3HQ, 2Q以及T的慢光電子頻譜(SPES)。論文的最後一部分開發了一種高效新穎的理論計算程式,專門用於解二維甲基扭轉運動的薛定諤方程。該程式能極大地減少花費在解析扭轉能及波函數的薛定諤方程上的時間,並在對丙酮及正-/反-2-丁烯及它們陽離子的二維甲基扭轉作用的研究中得到了驗證。此程式計算得出的扭轉頻率與實驗值吻合,這證明了其之高效性及可靠性。

    Research areas

  • Mathematics, Chemistry