Density-functional study of lanthanum, ytterbium, and lutetium dimers

La-2, Yb-2, and Lu-2 have been studied by use of the density-functional methods B3LYP, BLYP, B3PW91, BHLYP, BP86, B3P86, MPW1PW91, and PBE1PBE. In these density-functional methods, the exchange functional is from either Becke's three-parameter HF-DFT hybrid exchange functional (B3), pure DFT exchange functional of 1988 (B), a modification of the half-and-half HF/DFT hybrid method (BH), Perdew-Wang 1991 (PW91), or Barone's modified PW91 (MPW1), while the correlation functional is from either Lee, Yang, and Parr (LYP), Perdew-Wang 1991 (PW91), or Perdew 86 (P86). PBE1PBE is the generalized-gradient-approximation exchange-correlation functional of Perdew, Burke, and Ernzerhof. For La-2, the calculated bond distance is in reasonable agreement with the experiment, but the calculated vibrational frequency is underestimated significantly compared with the experiment. Only BP86 and B3P86 have the best performance in reproducing the experimental dissociation energy for La-2. For the van der Waals dimer Yb-2, three functionals, B3LYP, BLYP, and BHLYP have excellent performance in reproducing the spectroscopic constants compared with both the experiment and previous theoretical studies.

Ground state of lutetium dimer by density functional methods

Bond distances, vibrational frequencies and dissociation energies for the ground state of Lu-2 were studied by density functional methods B3LYP, B3PW91, BLYP, BHLYP, BP86, B3P86, MPW1PW91, PBE1PBE and SVWN with CEP-121G and SDD basis sets. Singlet state is predicted to be the most stable. CEP-121G has a better overall performance than SDD. At CEP-121G basis set, all density functional methods used in this study perform well in reproducing the spectroscopic constants.

Substitution effect of nitrogen atoms with carbon atoms in porphyrin on the electronic structure and excited states properties

Density functional theory (DFT) electronic structure calculations were carried out to predict the structures and the absorption and emission spectra for porphyrin and a series of carbaporphyrins-carbaporphyrin, adj-dicarbaporphyrin, opp-dicarbaporphyrin, tricarbaporphyrin and tetracarbaporphyrin. The ground- and excited-state geometries were optimized at the B3LYP/6-31g(d) and CIS/6-31g(d) level, respectively. The optimized ground-state geometry and absorption spectra of porphyrin, calculated by DFT and time-dependent DFT (TDDFT), are comparable with the available experimental values. Based on the optimized excited-state geometries obtained by CIS/6-31g(d) method, the emission properties are calculated using TDDFT method at the B3LYP/6-31g(d) level. The effects of the substitution of nitrogen atoms with carbon atoms at the center positions of porphyrin are discussed. The results indicate that the two-pyrrole nitrogens are important to the chemical and physical properties for porphyrin.

Geometries and electronic properties of AunPdm (n=1-4, m =-1, 0, 1) clusters

Possible conformers for AunPdm (n = 1-4, m = -1, 0, 1) clusters have been presented and studied by use of density functional theory. The results indicate that for n = 2, linear conformer with C-infinityv symmetry is the most stable for anion species, while for cation and neutral species, conformer with C-2v symmetry is the most stable. For n = 3, 4, conformers with C-2v symmetry (kite-shape) are energetically favored. The calculated electron affinities (EAs) and vertical detachment energies (VDEs) are in good agreement with experiments for n = 1-4. It is also interesting to note that for even n (n = 2, 4), the most stable conformers do not give the best agreement between calculated and experimental EA and VDE values, while for odd n (n = 3), the lowest energy conformer also gives the best agreement. The ionization potentials (IPs) of AunPd clusters are calculated as well.

Addition reactions of nitrones on the reconstructed C(100)-2 x 1 surfaces

In this paper, the reactions of nitrone, N-methyl nitrone, N-phenyl nitrone and their hydroxylamine tautomers (vinyl-hydroxylamine, N-methyl-vinyl-hydroxylamine and N-phenyl-vinyl-hydroxylamine) on the reconstructed C(100)-2 x 1 surface have been investigated using hybrid density functional theory (B3LYP), Moller-Plesset second-order perturbation (MP2) and multi-configuration complete-active-space self-consistent-field (CASSCF) methods. The calculations showed that all the nitrones can react with the surface "dimer" via facile 1.3-dipolar cycloaddition with small activation barriers (less than 12.0 kJ/mol at B3LYP/6-31g(d) level). The [2+2] cycloaddition of hydroxylamine tautomers on the C(100) surface follows a diradical mechanism. Hydroxylamine tautomers first form diradical intermediates with the reconstructed C(I 00)-2 x I surface by overcoming a large activation barrier of 50-60 kJ/mol (B3LYP), then generate [2+2] cycloaddition products via diradical transition states with negligible activation barriers. The surface reactions result in hydroxyl or amino-terminated diamond surfaces, which offers new opportunity for further modifications. (C) 2007 Elsevier B.V. All rights reserved.

Addition reaction of nitrones on the reconstructed Si(100)-2 x 1 surface

The reaction of nitrone, N-methyl nitrone, and their hydroxylamine tautomers (vinyl-hydroxylamine and N-methyl vinyl-hydroxylamine) on the reconstructed Si(100)-2 x 1 surface has been investigated by means of hybrid density functional theory (B3LYP) and Moller-Plesset second-order perturbation (MP2) methods. The calculations predicted that both of the nitrones should react with the surface dimer via facile concerted 1,3-dipolar cycloaddition leading to 5-member-ring compounds. The reaction of hydroxylamine tautomers on the Si(100) surface follows pi-complex (intermediate) mechanism. For the reaction of N-methyl vinyl-hydroxylamine, the pi-complex intermediate undergoes [2+2] cycloaddition leading to a 4-member-ring compound. But in the reaction of vinyl-hydroxylamine, the intermediate undergoes H-migration reaction ("ene" reaction) resulting in the oxime-terminated Si surface. All the surface reactions result in the hydroxyl-terminated silicon surfaces, which are very useful for the further modification of the semiconductor.

Theoretical study of interaction between atoms of Au, Ag, Cu and clean Si(111) surface

To evaluate the interactions between the atoms of An, Ag and Cu and clean Si(111) surface, two types of silicon clusters Si4H7 and Si16H20 together with their metal complexes were studied by using hybrid (U)B3LYP density functional theory method. Optimized geometries and energies on different adsorption sites indicate that: (1) the binding energies at different adsorption sites are large (ranging from similar to 1.2 to 2.6 eV depend on the metal atoms and adsorption sites), suggesting a strong interaction between metal atom and silicon surface; (2) the most favorable adsorption site is the on top (T) site. Mulliken population analysis indicated that in the system of on top (T) site, a covalent bond is formed between metal atom and dangling bond of surface Si atom. (c) 2006 Elsevier B.V. All rights reserved.

地幔压力下CaSiO3 Perovskite状态方程和弹性常数的第一性原理研究

In the past decade density functional theory (DFT) has made its way from a peripheral position in quantum chemistry to center. Of course the often excellent accuracy of the DFT based methods has provided the primary driving force of this development. This dissertation is devoted to the study of physical and chemical properties of planetary materials by first-principle calculation. The concerned properties include the geometry, elastic constants and anisotropy. In the first chapter, we give a systematic introduction to theoretical background and review its progress. Development of quantum chemistry promotes the establishment of DFT. Theorem of Hohenberg-Kohn is the fundament of DFT and is developed to Kohn-Sham equation, which can be used to perform real calculations. Now, new corrections and extensions, together with developed exchange-correlation, have made DFT more accurate and suitable for larger systems. In the second chapter, we focus on the calculational methods and technical aspects of DFT. Although it is important to develop methods and program, external package are still often used. At the end of this chapter, we briefly some widely used simulation package and the application of DFT. In the third chapter, we begin to focus on properties of real materials by first principles calculation. We study a kind of minerals named Ca perovskite, investigate its possible structure and anisotropy at Earth’s mental condition. By understanding and predicting geo-physically important materials properties at extreme conditions, we can get the most accurate information to interpret seismic data in the context of likely geophysical processes.

压力和铁含量对铁方镁石(Mg1-xFex)O(x<=0.25)弹性常数影响的第一性原理研究

By first principle methods based on density functional theory (DFT),the equation of state(EOS) and elastic constants of both periclase and ferropericlase are calculated. The pressure and iron doping effects on the elastic constants of ferropericlase are investigated systematically. Firstly, we calculate the elastic constants of periclase and compare the obtained results with experimental data and other theoretical calculations, which shows a encouraging consistence and demonstrates the practicability of first-principle methods. Secondly, by adding iron into periclase crystal model, we build up ferropericlase with iron contents ranging from 0% to 25% mole percent. The corresponding elastic constants are calculated in a large pressure range(0~120GPa). Emphatically, the strong correlation of 3d electrons in transitional elements, such as iron, is difficult to treat in first-principle methods for a long time. The current solution is to make additional correction. During the initial stage of this study, the strong correlation of 3d electrons in iron is not considered, and we observed that addition of iron decreases the volume of ferropericlase, which is totally contradictory to the experimental data. By applying LDA+U approximation in order to solve the strongly correlated 3d electron of iron, we observed the expansion of volume by iron as expected. On the basis of the LDA+U approximation, the elastic constants of ferropericlase are calculated. After a detailed analysis of data obtained from theoretical calculations, we have reached the following conclusions:(1)pressure imposes positive effects on all elastic constants, and the degree of effects is C11>C12>C44. (2) Iron has no distinctive effects on C11 and C12, although some fluctuations are observed around 60GPa. However, iron has obvious softening effects on C44 The softening effects on C44 are intensified as pressure increases. Above the 100GPa, the effects increase greatly, even surpasses the pressure's positive effects in ferropericlase crystal models with iron mole percent of having 12.5%, 18.75% and 25% iron content. (3)As to the modulus deprived from elastic constants, iron has no effect on the adiabatic bulk module BS, only a little fluctuation around 60GPa. We find iron's softening effects on shear modulus G. (4)We find out that, compared with low iron content, elastic constants with iron content approaching 25mole% is consistently fluctuated，which may be caused by the limitations of the LDA+U approximation method itself. (5)We investigate the pressure and Fe doping effects on elastic anisotropy factor（A=(2C44+C12-C11)/C11） of ferropericlase and find out that iron contents will lower the critical isotropic pressure. At the same pressure, when the pressure is below the isotropic pressure, iron softens the anisotropy factor ; when pressure surpasses the isotropic pressure, iron increases the anisotropy factor.

Tensor density matrix theory for determining population and alignment of symmetric top molecule using rotationally unresolved fluorescence

General expressions used for transforming raw laser-induced fluorescence (LIF) intensity into the population and alignment parameters of a symmetric top molecule are derived by employing the density matrix approach. The molecular population and alignment are described by molecular state multipoles. The results are presented for a general excitation-detection geometry and then applied to some special geometries. In general cases, the LIF intensity is a complex function of the initial molecular state multipoles, the dynamic factors and the excitation-detection geometrical factors. It contains a population and 14 alignment multipoles. How to extract all initial state multipoles from the rotationally unresolved emission LIF intensity is discussed in detail.

A combined DFT and SCRF study of solvent effects on 4-methyl-3-penten-2-one

The IR spectrum of 4-methyl-3-penten-2-one is interpreted with the aid of normal coordinate calculations within the Onsager self-consistent reaction field (SCRF) model, using a density functional theory (DFT) method at the Becke3LYP/6-31G* level. The solvent effects on the geometry, energy, dipole moment, and vibrational frequencies of 4-methyl-3-penten-2-one in the solution and in the liquid phase are calculated using the Onsager SCRF model. The calculated vibrational frequencies in the liquid-phase are in good agreement with the experimental values. The solvent reaction field has generally weak influence. For the two main bands of C=C and C=O mixed vibrational modes, small frequency shifts (5-6 cm(-1)), but relatively large changes in IR intensities (up to 101 km mol(-1) in the liquid phase) are found. (C) 1999 Elsevier Science BV. All rights reserved.