对含重元素体系的接合二分量-标量相对论密度泛函计算方法

在相对论密度泛函ZORA方法的基础上,提出一种用于含重元素体系的接合二分量-标量相对论密度泛函计算方法.对于只含少数几个重元素的较大体系,仅对其中旋轨耦合作用强的重元素作二分量相对论计算,而对体系的其余部分则作标量相对论计算,通过对动能矩阵元的近似处理实现两种计算的接合.对一系列含6p区重元素分子进行计算的结果表明,当非重元素是第三周期以前的元素时,此方法与二分量ZO-RA方法的计算结果吻合得很好.当非重元素为第四周期元素时,计算结果有一定偏差,表明在后一种情况下旋轨耦合作用已比较显著,但误差仍在目前近似密度泛函计算的精度范围内.此方法可以有效地节省计算量,而且避免了Dyall方法的缺点.     

An experimental and computational NMR study of organometallic nine-membered rings: Trinuclear silver(I) complexes of pyrazolate ligands

This work reports the calculation of the nuclear magnetic resonance (NMR) chemical shifts of eight trinuclear Ag(I) complexes of pyrazolate ligands using the relativistic program ZORA. The data from the literature concern exclusively ¹H, ¹³C, and ¹⁹F nuclei. For this reason, one of the complexes that is derived from 3,5-bis-trifluoromethyl-1H-pyrazole has been studied anew, and the ¹⁵N and ¹⁰⁹Ag chemical shifts determined for the first time in solution. Solid-state NMR data of this compound have been obtained for some nuclei (¹H, ¹³C, and ¹⁹F) but not for others (¹⁴N, ¹⁵N, and ¹⁰⁹Ag).     

Quantum relativistic investigation about the coordination and bonding effects of different ligands on uranyl complexes

The coordination and bonding effects of equatorial ligands such as fluoride (F⁻), chloride (Cl⁻), cyanide (CN⁻), isocyanide (NC⁻), and carbonate (CO₃⁻²) on uranyl dication (UO₂²⁺) has been studied using relativistic density functional theory. The ZORA Hamiltonian was applied for the inclusion of relativistic effects taking into account all the electrons for the optimization and the explicit inclusion of spin–orbit coupling effects. Geometry optimizations including the counterions and frequencies analysis were carried out with PW91 and PBE functional. Solvents effects were considered by using the conductor like screening model (COSMO) for water and acetonitrile. The Time-Dependent Density Functional Theory (TDDFT) was used to calculate the excitation energies with GGA SAOP functional and the electronic transitions were analyzed using double group irreducible representations. The theoretical results are in a good agreement with experimental IR, Raman and EXAFS spectra and previous theoretical results. New information about the effect of different (donor and acceptors) ligands on the bonding of uranyl ion and on the electronic transitions involved in these complexes is provided with a possible impact on the understanding of the uranyl coordination chemistry.     

Theoretical calculations of the chemical shifts of cyclo[n]phosphazenes for n = 2, 3, 4 and 5 (X2PN)n with X = CH3, F,Cl and Br: the effect of relativistic corrections

Abstract

Di, tri, tetra and pentacyclophosphazenes substituted on the phosphorus atoms by CH₃, F, Cl and Br atoms corresponding to (X₂PN)_n structures have been studied theoretically at the B3LYP/6-311++G(d,p) level. After a brief discussion of their geometries comparing them to those of the conjugated carbocycles, (CH)_n, of the same size, the absolute shieldings calculated with the GIAO and ZORA approximations will be reported. For the Cl and mainly for the Br substituted cyclo[n]-phosphazenes, relativistic corrections are absolutely necessary for ³¹P and useful for ¹⁵N chemical shifts.     

HFI and DFT study of the bonding in complexes of halogen and interhalogen diatomics with Lewis base

We have analyzed by means of DFT calculations with use of the pseudo-potential the nuclear quadrupole coupling constants of a range of XYB complexes (n aσ type in Mulliken notation) formed between diatomic interhalogen molecules XY and Lewis bases B. The geometrical parameters, rotational and halogen nuclear quadrupole coupling constants obtained by these calculations substantially corresponded to the data of microwave spectroscopy in the gas phase. An analysis of the quality of the calculations that employ the pseudo-potential and the expanded basis set for the halogen compounds was carried out. The ZORA model is shown to be a viable alternative to the computationally demanding BH and HLYP model for the calculation of halogen and nitrogen coupling constants in molecules. In addition, the ZORA model, in contrast to the pseudo-potential model, leads to realistic values of iodine nuclear quadrupole coupling constants. From electron partitioning analyses and Klopman's approach it follows that for the IClB complexes the electrostatic bonding is predominant relative to covalent bonding.     

Quantum‐chemical analyses of aromaticity,UV spectra,and NMR chemical shifts in plumbacyclopentadienylidenes stabilized by Lewis bases

We carried out a series of zeroth‐order regular approximation (ZORA)‐density functional theory (DFT) and ZORA‐time‐dependent (TD)‐DFT calculations for molecular geometries, NMR chemical shifts, nucleus‐independent chemical shifts (NICS), and electronic transition energies of plumbacyclopentadienylidenes stabilized by several Lewis bases, (Ph)₂(^tBuMe₂Si)₂C₄PbL₁L₂ (L₁, L₂ = tetrahydrofuran, Pyridine, N‐heterocyclic carbene), and their model molecules. We mainly discussed the Lewis‐base effect on the aromaticity of these complexes. The NICS was used to examine the aromaticity. The NICS values showed that the aromaticity of these complexes increases when the donation from the Lewis bases to Pb becomes large. This trend seems to be reasonable when the 4n‐Huckel rule is applied to the fractional π‐electron number. The calculated ¹³C‐ and ²⁰⁷Pb‐NMR chemical shifts and the calculated UV transition energies reasonably reproduced the experimental trends. We found a specific relationship between the ¹³C‐NMR chemical shifts and the transition energies. As we expected, the relativistic effect was essential to reproduce a trend not only in the ²⁰⁷Pb‐NMR chemical shifts and J[Pb‐C] but also in the ¹³C‐NMR chemical shifts of carbons adjacent to the lead atom. © 2014 Wiley Periodicals, Inc.     

QM/MM study of aqueous solvation of the uranyl fluoride [UO2F4(2-)] complex

The aqueous solvation of the uranylfluoride complex [UO(2)F(4) (2-)] was studied using full quantum mechanical (QM) and hybrid QM/molecular mechanics (MM) methods. Inclusion of a complete first solvation shell was found necessary to reproduce the experimentally observed heptacoordination of uranium. An efficient and accurate computational model is proposed that consists of structure optimization of the coordinated uranium complex as QM region, followed by single-point full QM calculations to compute relative energies. This method is proven feasible for studies of large solvated actinide complexes.     

改进的相对论量子化学计算ZORA方法

提出一种改进的ZORA(Zeroth-OrderRegularApproximationtotheDiracEquation)方法,其单电子方程为：[σ·p(c^2/2c^2-V~0)σ·p+V(r)]ψ=εψ。式中V~0为空间限域的势能函数：V~0(r=~A∑V~0^A(r~A),r~A=|r-R~A|,V~0^A(r~A)=V^A(r~A){1+exp[α(r~A-r~0^A]}^-^1。其中A表示分子的某个组成原子,R~A为A原子的位置矢量,V^A(r~A)为自由A原子的势函数,α和r~0^A为参数。改进的ZORA方法具有原来方法的所有优点,避免了原有ZORA方法因不满足标度变换不变性带来的缺陷,而且计算过程简单。具体计算表明,通过适当选择参数α和r~0^A,用本研究提出来的方法,在计算分子几何结构和键合能时,基本上消除了ZORA方法由于标度变换依赖性产生的误差。     

All-electron scalar relativistic basis sets for the elements Rb–Xe

Segmented all-electron relativistically contracted (SARC) basis sets are presented for the elements ₃₇Rb–₅₄Xe, for use with the second-order Douglas–Kroll–Hess approach and the zeroth-order regular approximation. The basis sets have a common set of exponents produced with established heuristic procedures, but have contractions optimized individually for each scalar relativistic Hamiltonian. Their compact size and loose segmented contraction, which is in line with the construction of SARC basis sets for heavier elements, makes them suitable for routine calculations on large systems and when core spectroscopic properties are of interest. The basis sets are of triple-zeta quality and come in singly or doubly polarized versions, which are appropriate for both density functional theory and correlated wave function theory calculations. The quality of the basis sets is assessed against large decontracted reference basis sets for a number of atomic and ionic properties, while their general applicability is demonstrated with selected molecular examples.