Density Functional Theory Study on Spin States of LaCoO3 at Room Temperature

The electronic structure of the perovskite LaCoO3 at room temperature structure （293 K） was calculated by using PBE, PBE＋U and HSE. Different spin configurations have been considered. Our calculations showed that the choice of the Hubbard U parameter in DFT＋U and mixing factor α in HSE significantly influenced the band gap as well as relative energies. For the spin exited states, the optimal value for U and α were 3.0 eV and 0.05, respectively. Our calculation also emphasized that when U〉5.0 eV, PBE＋U would lead to unreasonable electronic structure and energy order.     

Experimental and Theoretical Study of Reactions between Manganese Oxide Cluster Cations and Hydrogen Sulfide

Manganese oxide cluster cations Mnm180n＋ were prepared by laser ablation and reacted with hydrogen sulfide （H2S） in a fast flow reactor under thermal collision conditions. A time-of-flight mass spectrometer was used to detect the cluster distributions before and after the interactions with H2S. The experiments suggest that oxygen-for-sulfur （O/S） ex- change reaction to release water took place in the reactor for most of the manganese oxide cluster cations： MnmlSOn＋＋H2S→Mnm18On-1S＋＋H218O. Density functional theory cal- culations were performed for reaction mechanisms of Mn202＋＋H2S, Mn203＋＋H2S, and Mn204＋＋H2S. The computational results indicate these O/S exchange reactions are both thermodynamically and kinetically favorable, thus in good agreement with the experimental observations. The O/S exchange reactions identified in this gas-phase cluster study parallel similar behavior of related condensed phase reaction systems.     

Frist-principles Band Structures Calculation of Tin-phthalocyanine

We adopt the density function theory with generalized approximation by the Beeke exchange plus Lee-Yang-Parr correlation functional to calculate the electronic first-principles band structure of tin-phthalocyanine （SnPc）. The intermolecular interaction related to transport behavior was analyzed from the F-point wave function as well as from the bandwidths and band gaps. From the calculated bandwidths of the frontier bands as well as the effective masses of the electron and hole, it can be concluded that the mobility of the electron is about two times larger than that of the hole. Furthermore, when several bands near the Fermi surface are taken into account, we find that the interband gaps within the unoccupied bands are generally smaller than those of the occupied bands, indicating that the electron can hop from one band to another which is much easier than the hole. This may happen through electron-phonon coupling for instance, thus effectively yielding an even larger mobility for the electron than for the hole. These facts indicate that in SnPc the electrons are the dominant carriers in transport, in contrast to most organic materials.     

Cyclic M（S02） （M=Zn,Cd） and its Anions： Matrix Infrared Spectra and DFT Calculations

Reaction of laser ablated zinc and cadmium atoms with SO2 molecules was studied by low temperature matrix isolation infrared spectroscopy. Cyclic M（SO2） and anion M（SO2）-（M=Zn, Cd） were produced in excess argon and neon, which were identified by 34SO2 and S18O2 isotopic substitutions. The observed infrared spectra and molecular structures were confirmed by density functional theoretical calculations. Natural charge distributions indicated significant electron transfer from s orbitals of zinc or cadmium metal atom to S02 ligand and cyclic M（SO2） complexes favored ＂ion pair＂ M＋（SO2）-formation, which were trapped in low temperature matrices. In addition Zn-O or Cd-O bond in M（SO2） exhibited strong polarized covalent character. Reaction of Hg atom with SO2 was also investigated, but no reaction product was observed, due to the relativistic effect that resulted in the contraction of 6s valence shell and high ionization potential of Hg atom.     

Infrared Photodissociation Spectroscopy of Ti＋（CO2）2Ar and Ti＋（CO2）n （n=3-7） Complexes

Ti＋（CO2）2Ar and Ti＋（CO2）n （n=3-7） complexes are produced by laser vaporization in a pulsed supersonic expansion. The ion complexes of interest are each mass-selected in a time- of-flight spectrometer, and studied with infrared photodissociation spectroscopy. For each complex, a sharp band in the CO stretching frequency region is observed, which confirms the formation of the OTi＋CO（CO2）~_l oxide-carbonyl species. Small OTi＋CO（CO2）~_1 complexes （n_〈5） exhibit CO stretching and antisymmetric CO2 stretching vibrational bands that are blue-shifted from those of free CO and CO2. The experimental observations indicate that the coordination number of CO and CO2 molecules around TiO＋ is five. Evidence is also observed for the presence of another electrostatic bonding Ti＋（CO2）2 structural isomer for the Ti＋（CO2）2Ar complex, which is characterized to have a bent OCO-Ti＋-OCO structure stabilized by argon coordination.     

DFT Study on Homolytic Dissociation Enthalpies of C-I Bonds

The C-I bond dissociation enthalpies （BDE） of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD（T） with extrapolated basis set as well as a number of density functional theory methods. After systematic evaluation of the theoretical results against available experimental C-I BDEs, it was found that the MPW LYPIM method gave the lowest root mean square error. We, therefore, used this method to examine the substituent effects on different categories of C（sp3）-I and C（sp2）-I bonds. Fur thermore, the remote substituent effects on the C-I BDEs of substituted iodobenzenes and substituted （iodomethyl）benzenes were also investigated at the same level. The C-I BDEs of typical heteroaromatic iodides including five-membered and six-membered heterocyclic iodides were also examined.     

Theoretical Investigation on the Absence of Spore Photoproduct Analogue at Cytosine-Thymine Site

As a well known DNA photolesion product, the special UV induced pyrimidine dimmer called spore photoproduct （SP）, has aroused strong research interests. The SP formation was reported solely between two adjacent thymidine residues. It remains unclear in pervious experimental observations why there is an absence of the cytosine-derived SP-like photoprod- uct formation at the cytosine containing DNA strand, although the cytosine residue holds great similarity to thymine in terms of molecular structure. From a theoretical perspec- tive, we have explored this issue in this work by means of density functional theory at the B3LYP/6-311＋＋G（d,p） //B3LYP/6-31G（d,p） level for the DNA dinucleotide fragment, cy- tosine phosphate thymine （CpT）. Key factors blocking the formation of the SP-like product between two adjacent cytosine and thymidine residues are revealed. Instead of undergoing photochemical SP reaction, a photophysical deactivation pathway back to the ground state turns out to be favorable for the CpT dinucleotide fragment.     

Theoretical Characterization of Chiral Carbon Nanotube Encapsulating Ellipsoidal C70

The molecular orientation of ellipsoidal C70 in carbon nanotubes is carefully studied by first principles calculations. Using （14, 7） single-wall carbon nanotube （SWCNT） as a prototype material, we explored that the weak chemical interaction between SWCNT and C70 was the crucial factor to determine the molecular orientation. However, the small energy difference makes the distinguishment of two possible molecular orientations difficult. By simulating scanning tunneling microscope images and optical properties, we found that local electronic states sensitively depended on the molecular orientation of ellipsoidal C70, which provided a practical way of using scanning tunneling microscope to recognize the molecular orientation of ellipsoidal C70.     

Sequential Observation of Alkali-halide Gas Phase Clusters in High Resolution TOF-MS and Prediction of Their Structures

Alkali halide clusters are interesting model systems that can provide information about how crystal properties evolve. To study these properties, a high-resolution atmospheric pressure inlet time-of-flight mass spectrometry （APi-TOF-MS） study of the sequential sodium halides series, C1-（NaC1）n and Br-（NaBr）m, has been reported, and the viability of the APi-TOF- MS equipped with an electrospray ionization source in determining cluster compositions has been demonstrated. The isotopic patterns were well resolved, as n=4 and 7 were determined to be the magic numbers for C1-（NaC1）n clusters, which were particularly abundant in the mass spectra. A global minimum search based on density functional theory enabled basin hopping yield the most stable structures for the mentioned series. The structures exhibit several distinct motifs which can be roughly categorized as linear chain, rock salt, and hexag- onal ring. This work provides an effective way to discover and elucidate the nonstoichiometry sodium halide clusters. These clusters possess very high vertical detachment energies and are generally called as superhalogens, which play important roles in chemistry because they are widely used in the synthesis of new classes of charge-transfer salts.     

Theoretical Investigation on Interaction between Guanine and Luteolin

The interacting patterns of the luteolin and guanine have been investigated by using the density functional theory B3LYP method with 6-31＋G＊ basis set. Eighteen stable structures for the luteolin-guanine complexes have been found respectively. The results indicate that the complexes are mainly stabilized by the hydrogen bonding interactions. Meanwhile, both the number and strength of hydrogen bond play important roles in determining the stability of the complexes which can form two or more hydrogen bonds. Theories of atoms in molecules and natural bond orbital have also been utilized to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes which were corrected by basis set superposition error are 6.04-56.94 kJ/mol. The calculation results indicate that there are strong hydrogen bonding interactions in the luteolin-guanine complexes. We compared the interaction between luteolin and four bases of DNA, and found luteolin-thymine was the strongest and luteolin-adenine was the weakest. The interaction between luteolin and DNA bases are all stronger than luteolin-water.     

Analysis of Potential Energy Surface for Butanone Isomerization

The potential energy surfaces for butanone isomerization have been investigated by density function theory calculation. Six main reaction pathways are confirmed using the intrinsic reaction coordinate method, and the corresponding isomerization products are 1-buten-2-ol, 2-buten-2-ol, butanal or 1-buten-l-ol, methyl 1-propenyl ether, methyl allyl ether, and ethyl vinyl ether, respectively. Among them, there are three pathways through butylene oxide, indicating butylene oxide is an important intermediate product during butanone isomer ization. The calculated vertical ionization energies of the reactant and its products are in a good agreement with the experimental values available. From the consideration for the relative energies Of transition states and the number of high-energy barriers we infer that the reaction pathway butanone-＊l-buten-2-ol---2-buten-2-oi is the most competitive. The obtained results are informative for future studies on isomerization of ketone molecules.     

Analytical Bond-order Potential for hcp-Y

The lattice parameters, elastic constants, cohesive energy, structural energy differences, as well as the properties of point defects and planar defects of hexagonal closepacked yttrium （hcpY） have been studied with ab initio density functional theory for constructing an ex tensive database. Based on an analytical bondorder poial scheme, empirical manybody interatomic potential for hcpY has been developed. The model is fitted to some properties of Y, e.g., the lattice parameters, elastic constants, bulk modulus, cohesive energy, vacancy formation energy, and the structural energy differences. The present potential has ability to reproduce defect properties including the selfinterstitial atoms formation energies, vacancy formation energy, divacancy binding energy, as well as the bulk properties and the thermal dynamic properties.     

Energetic preferences for alpha,beta versus beta,gamma unsaturation

Density functional theory has been applied at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level to examine the energetics of alpha,beta- versus beta,gamma-unsaturation for some common organic functional groups. Specifically, the relative stabilities of allyl-X (H2C=CHCH2X) and 1-propenyl-X (H3CCH=CHX) isomers have been computed for X = methyl, vinyl, phenyl, formyl, acetyl, methoxy, methylthio, methylsulfinyl, methylsulfonyl, sulfamoyl, and methoxysulfonyl, and the results are compared to available experimental data. The intrinsic preference of 3 kcal/mol for the 1-propenyl isomer when X = CH3 is exceeded by 2-4 kcal/mol for first-row conjugating groups, but it is not met for the sulfur-containing groups. In particular, alpha,beta-unsaturation is favored by less than 1 kcal/mol for the sulfone and sulfonamide analogues, while it is preferred by 8 kcal/mol for the vinyl-substituted case. Detailed structural results and torsional energy profiles are also reported.     

Correlation between the rate order and the number of molecules in the reaction of trimethyl phosphite with water in acetonitrile solvent

Density functional theory calculations of the title reaction, P(OCH?)? + (H?O)(n) in CH?CN, were conducted, where n is the number of water molecules. Two routes, the routes suggested by (A) Aksnes and (B) Arbuzov, were traced with various n values. Both routes consist of two transition states (TSs) and one intermediate. Route B was found to be more likely than route A. In the former, the activation free energy (ΔG(?)) of n = 3 is slightly smaller than that of n = 2. The n = 3 TS geometry is composed of a nucleophile H?O, a proton donor H?O, and an auxiliary one. Indeed, the geometry appears to be plausible for ready proton relays along hydrogen bonds, but it is inconsistent with the observed third-order rate constant. Catalytic water molecules were added to the n = 2 and 3 bond-interchange circuits. Then route B with n = 2 + 2 was found to be best. By n = 2 + 10 and n = 3 + 12 models, the n = 2 based route B was confirmed to be likely.     

How Effective Is the Single-point Energy Calculation in Investigating the Reaction Mechanisms？ New Decarboxylation Mechanism of Pyrrole-2-carboxylic Acid by Full Optimization with CPCM Solvation Model

The decarboxylation of pyrrole-2-carboxylic acid in acid solutions was elucidated by full optimization with the CPCM solvation model at the B3LYP/6-31 l＋＋G（d,p） level. Compared with the single-point energy calculation, CPCM full optimization is better to model solvent environments to gain reasonable reaction mechanisms. The π interactions play a significant role in the decarboxylation of pyrrole-2-carboxylic acid （R）. Firstly, the a hydrogen is protonated, but all of the carbonyl hydration pathways bear relatively higher energy barriers. The carbonyl group can rove over the pyrrole ring, but it does not lead to the speciation of pyrrole and protonated carbon dioxide for the latter is an energy-rich species. The decarboxylation mechanism proposed here is that, the protonated pyrrole-2-carboxylic acid （RH） decarboxylates via direct C-C bond cleavage with the aid of a water molecule to accommodate the proton on the carbonyl group.     

MP2, DFT and ab initio calculations on thioxanthone

Density functional theory (DFT), HF and MP2 calculations have been carried out to investigate thioxanthone molecule using the standard 6-31+G(d,p) basis set. The results of MP2 calculations show a butterfly structure for thioxanthone. The calculated results show that the predicted geometry can well reproduce the structural parameters. The predicted vibrational frequencies were assigned and compared with experimental IR spectra. A good harmony between theory and experiment is found. The theoretical electronic absorption spectra have been calculated using CIS method. ¹³C and ¹H NMR of the title compound have been calculated by means of B3LYP density functional method with 6-31+G(d,p) basis set. The comparison of the experimental and the theoretical results indicate that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

^3A＇ and ^3A＂ Energy Surfaces for the VS^＋ ＋ CO2→VO^＋ ＋ COS Reaction

The title reaction proceeds via a one- and two-step mechanism along the ^3A＂ and ^3A＇ surfaces, respectively. The ^3A＇ excited state surface has a lower barrier than the ^3A＂ ground state surface （11.6 and 16.0 kca1/mol, respectively）, We suggest that, at low energies, the reaction proceeds along the A＇ surface and then makes an intersystem crossing to the A＂ surface and yields the ground state product VO^＋（^3∑^-）, which may explain the small VO^＋ cross-section at low energies observed in the experiment     

Influence of non-metallic atoms on the absorption of amphetamines on B12N12 nano-cages

Structural Chemistry - Density functional theory (DFT) calculations at B3LYP/6-31+G(d) level were employed to investigate the influence of the non-metal encapsulation of the second row of the...     

Crystal Structure, Photoluminescence and Theoretical Studies of Diethyl 4,5-di（thienyl）- 3,6-bis（trimethylsilyl）phthalate

The crystal structure of the title compound, diethyl 4,5-di（thienyl）-3,6-bis（trime- thylsilyl）phthalate （C26H3404S2Si2, Mr = 530.83）, has been determined by single-crystal X-ray diffraction. The crystal belongs to the orthorhombic system, space group Pccn with a = 43.008（5）, b = 10.9000（12）, c = 11.9357（14） A, V= 5595.3（11） A3, Z = 8, F（000） = 2256, Dc= 1.260 mg/m3, p = 0.305 mm-1, T = 113（2） K, S = 1.090, R = 0.0413 and wR = 0.0969 for 5952 observed reflections with 1 〉 2o（/）. The benzene ring system is planar and makes dihedral angles of 63.7（2） and 72.5（4） with the two thienyl rings A （C（23）-C（26）, S（2）） and B （C（19）-C（22）, S（1））, respectively. The UV-vis absorption and fluorescence of the title compound were discussed. The molecular structure of the title compound has been optimized using DFT method at the B3LYP/6-31G（d） level. The computational results showed that the optimized geometer parameters are consistent well with the experiment data. The vertical ionization potential, vertical electron affinity and frontier orbitals were also discussed.