ChemInform Abstract: First‐Principles Calculations of the Structural,Electronic, Optical and Elastic Properties of the New Phosphors,Na2ZrF6 and K2ZrF6.

Na₂ZrF₆ and K₂ZrF₆ are characterized using the plane‐wave based first‐principles calculations.     

Interaction between RNA segment (adenine‐uracil) and model of protein unit (formamide): A density‐functional theory study

Various possible structures of adenine‐uracil‐formamide hydrogen‐bond complexes were optimized at 6‐311++G(d,p) level, and the binding energies of these complexes were also calculated at DFT B3LYP/6‐311++G(d,p) level. Eight stable cyclic structures being involved in the interaction are found on the potential energy surface. By analyzing the structure, NPA charge and interaction energy of complexes, we obtain the most stable geometry structure. The results show that the interactions between formamide and adenine‐uracil (A‐U) base pair affect the stabilities of the base pairs. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Phenomenological approach to compare the crystallization kinetics of isotactic polypropylene and polyamide‐6 under pressure

Reliable experimental data for semicrystalline polymers crystallized under pressure are supplied on the basis of a model experiment in which drastic solidification conditions are applied. The influence of the pressure and cooling rate on some properties, such as the density and microhardness, and on the product morphology, as investigated with wide‐angle X‐ray scattering (WAXS), is stressed. Results for isotactic polypropylene (iPP) samples display a lower density and a lower microhardness with increasing pressure over a wide range of cooling rates (from 0.01 to 20 °C/s). Polyamide‐6 (PA6) samples exhibit the opposite behavior, with the density and microhardness increasing at higher pressures over the entire range of cooling rates investigated (from 1 to 200 °C/s). A deconvolution technique applied to iPP and PA6 WAXS patterns has allowed us to evaluate the final phase content and to assess the crystallization kinetics. A negative influence of pressure on the α‐crystalline phase crystallization kinetics can be observed for iPP, whereas a slightly positive influence of pressure on the crystallization kinetics of PA6 can be noted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 153–175, 2002     

Analysis of ToF‐SIMS spectra of poly(2‐vinylpyridine) and poly(4‐vinylpyridine) with density functional theory calculations

The time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) positive and negative ion spectra of poly(2‐vinylpyridine) (P2VP) and poly(4‐vinylpyridine) (P4VP) were analyzed using density functional theory calculations. Most of the ions from these structural isomers shared the same accurate mass, but had different relative abundance. This could be attributed to the fact that from a thermodynamics perspective, the disparity in the molecular structures can affect the ion stability if we assume that they shared the same mechanistic pathway of formation with similar reaction kinetics. The molecular structures of these ions were assigned, and their stability was evaluated based on calculations using the Kohn‐Sham density functional theory with Becke's 3‐parameter Lee‐Yang‐Parr exchange‐correlation functional and a correlation‐consistent, polarized, valence, double‐zeta basis set for cations and the same basis set with a triple‐zeta for anions. The computational results agreed with the experimental observations that the nitrogen‐containing cations such as C₅H₄N⁺ (m/z = 78), C₈H₇N^+· (m/z = 117), C₈H₈N⁺ (m/z = 118), C₉H₈N⁺ (m/z = 130), C₁₃H₁₁N₂⁺ (m/z = 195), C₁₄H₁₃N₂⁺ (m/z = 209), C₁₅H₁₅N₂⁺ (m/z = 223), and C₂₁H₂₂N₃⁺ (m/z = 316) ions were more favorably formed in P2VP than in P4VP due to higher ion stability because the calculated total energies of these cations were more negative when the nitrogen was situated at the ortho position. Nevertheless, our assumption was invalid in the formation of positive ions such as C₆H₇N⁺˙ (m/z = 93) and C₈H₁₀N⁺ (m/z = 120). Their formation did not necessarily depend on the ion stability. Instead, the transition state chemistry and the matrix effect both played a role. In the negative ion spectra, we found that nitrogen‐containing anions such as C₅H₄N^? (m/z = 78), C₆H₆N^? (m/z = 92), C₇H₆N^? (m/z = 104), C₈H₆N^? (m/z = 116), C₉H₁₀N^? (m/z = 132), C₁₃H₁₁N₂^? (m/z = 195), and C₁₄H₁₃N₂^? (m/z = 209) ions were more favorably formed in P4VP, which is in line with our computational results without exception. We speculate that whether anions would form from P2VP and P4VP is more dependent on the stability of the ions.     

Density functional theory study of tautomerization of 2‐aminothiazole in the gas phase and in solution

The amino/imino tautomeric equilibrium in the isolated, mono‐, di‐, and trihydrate forms and dimer of 2‐aminothiazole, and the effects of hydration or self‐assistance on the transition state structures corresponding to proton transfer from the amino to imino form, have been investigated by the B3LYP method in conjunction with 6‐31+G(d,p) and 6‐311+G(3df,2p) basis sets in the gas phase and in solution. The amino form has been found to be the predominant tautomer. The tautomeric barrier heights for water‐ and self‐assisted tautomerization reactions are significantly lower than that from the amino to imino form by the intramolecular proton transfer, showing the catalytic effect of water molecule(s) and the important role of 2‐aminothiazole itself for intermolecular proton transfer. Comparison between the tautomeric barriers demonstrates that the self‐association tautomerization through the dimerization is the most favorable pathway. Bulk solvent effects have been taken into account using the polarizable continuum model (PCM) of water and CCl₄. The polar medium is favorable for the population of the imino form. The amino/imino equilibrium is also analyzed using the aromaticity index nucleus‐independent chemical shift (NICS); the NICS values for the amino form (about ?10 ppm) are more negative than the imino species (about ?8 ppm), showing that the amino form is more stable. The time‐dependent density functional theory (TDDFT) calculations of electronic absorption spectra suggest that the λ_max of dimer is 255 nm. The oscillator strength of the imino forms is less than the amino form, and increases with the polarity of the solvents. All calculations for the tautomerization of 2‐aminothiazole are in reasonable line with the available experiments. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Time‐dependent density functional theory study of electronic spectrum property for carbazolyl–pyridinyl alternating copolymers

Three A‐B‐type fluorescent copolymers comprised of alternating carbazolyl and pyridinyl units, poly[(2,7‐(N‐(2‐ethylhexyl)carbazolyl)‐alt‐(3,5‐pyridinyl))](PEHCP‐35), poly[(2,7‐(N‐(2‐ethylhexyl)carbazolyl)‐alt‐(2,6‐pyridinyl))] (PEHCP‐26) and poly[(2,7‐(N‐(2‐ethyl‐hexyl)carbazolyl)‐alt‐(2,5‐pyridinyl))] (PEHCP‐25), are studied by means of the density functional theory (DFT/B3LYP/6‐31G). Based on the optimized geometries, the optical properties are calculated by employing time‐dependent density functional theory (TD‐DFT). The bandgaps and optical properties are saturated quickly in PEHCP‐35 and PEHCP‐26. It is known from experiment that PEHCP‐25 is actually an oligomer with a polymerization degree of 4. So the tetramers of PEHCP‐35, PEHCP‐26, and PEHCP‐25 are adopted to study the electronic and optical properties, and the calculated results are in close agreement with experiment. The calculated bandgaps of copolymers obtained from two ways, i.e., HOMO–LUMO gaps and the lowest excitation energies, decrease in the following order PEHCP‐35 > PEHCP‐26 > PEHCP‐25, the same trend as the data obtained from the edge of the electric band but different from the electrochemically obtained data from experiment (PEHCP‐25 > PEHCP‐26 > PEHCP‐35). The outcomes showed that, when excited, a charge transfer from carbazolyl unit to pyridinyl unit occurs, and the lumophor is mainly carbazolyl units. The UV absorption and emission wavelengths both exhibit bathochromic shifts: PEHCP‐35 < PEHCP‐26 < PEHCP‐25. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Rapid QM/MM approach for biomolecular systems under periodic boundary conditions: Combination of the density‐functional tight‐binding theory and particle mesh Ewald method

A quantum mechanical/molecular mechanical (QM/MM) approach based on the density‐functional tight‐binding (DFTB) theory is a useful tool for analyzing chemical reaction systems in detail. In this study, an efficient QM/MM method is developed by the combination of the DFTB/MM and particle mesh Ewald (PME) methods. Because the Fock matrix, which is required in the DFTB calculation, is analytically obtained by the PME method, the Coulomb energy is accurately and rapidly computed. For assessing the performance of this method, DFTB/MM calculations and molecular dynamics simulation are conducted for a system consisting of two amyloid‐β(1‐16) peptides and a zinc ion in explicit water under periodic boundary conditions. As compared with that of the conventional Ewald summation method, the computational cost of the Coulomb energy by utilizing the present approach is drastically reduced, i.e., 166.5 times faster. Furthermore, the deviation of the electronic energy is less than . © 2016 Wiley Periodicals, Inc.     

Density functional theory study of the interaction between 3‐nitro‐1,2,4‐triazole‐5‐one and ammonia

Two fully optimized geometries of 3‐nitro‐1,2,4‐triazol‐5‐one (NTO)–NH₃ complexes have been obtained with the density function theory (DFT) method at the B3LYP/6‐311++G** level. The intermolecular interaction energy is calculated with zero point energy (ZPE) correction and basis set superposition error (BSSE) correction. The greatest corrected intermolecular interaction of the NTO–NH₃ complexes is ?37.58 kJ/mol. Electrons in complex systems transfer from NH₃ to NTO. The strong hydrogen bonds contribute to the interaction energies dominantly. Natural bond orbital (NBO) analysis is performed to reveal the origin of the interaction. Based on vibrational analysis, the changes of thermodynamic properties from the monomer to complexes with the temperature ranging from 200 K to 800 K have been obtained using the statistical thermodynamic method. It is found that two NTO–NH₃ complexes can be produced spontaneously from NTO and NH₃ at normal temperature. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Application of zone‐folding approach to the first‐principles estimation of thermodynamic properties of carbon and ZrS2‐based nanotubes

A zone‐folding (ZF) approach is applied for the estimation of the phonon contributions to thermodynamic properties of carbon‐and ZrS₂‐based nanotubes (NTs) of hexagonal morphology with different chiralities. The results obtained are compared with those from the direct calculation of the thermodynamic properties of NTs using PBE0 hybrid exchange‐correlation functional. The phonon contribution to the stability of NTs proved to be negligible for the internal energy and small for the Helmholtz free energy. It is found that the ZF approach allows us an accurate estimation of phonon contributions to internal energy, but slightly overestimates the phonon contributions to entropy. © 2015 Wiley Periodicals, Inc.     

Effect of metal cations [Li+, Na+, K+, Be2+, Mg2+, and Ca2+] on the structure of 2‐(3′‐hydroxy‐2′‐pyridyl)benzoxazole: A theoretical investigation

Density functional theory calculations were performed at the B3LYP/6‐311++G(d,p) level to systematically explore the geometrical multiplicity and binding strength for the complexes formed by alkaline and alkaline earth metal cations, viz. Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ (Mⁿ⁺, hereinafter), with 2‐(3′‐hydroxy‐2′‐pyridyl)benzoxazole. A total of 60 initial structures were designed and optimized, of which 51 optimized structures were found, which could be divided into two different types: monodentate complexes and bidentate complexes. In the cation‐heteroatom complex, bidentate binding is generally stronger than monodentate binding, and of which the bidentate binding with five‐membered ring structure has the strongest interaction. Energy decomposition revealed that the total binding energies mainly come from electrostatic interaction for alkaline metal ion complexes and orbital interaction energy for alkaline earth metal ion complex. In addition, the electron localization function analysis show that only the Be? O and Be? N bond are covalent character, and others are ionic character. © 2012 Wiley Periodicals, Inc.     

N-甲基b-磺内酰胺氨解反应机理的理论研究

The aminolysis and the effect of water on the aminolysis processes of n-methyl β-sultam have been studied using density functional theory （DFF） method at the B3LYP/6-31G＊ level. The stationary structures and energies have been investigated for both reactions to find two different reaction channels. Specific and general solvent effects have been evaluated and the most favored pathway was found. The presence of solvent disfavors the reaction, whereas the participation of water in the aminolysis reaction plays a positive role and reduces the activation energy greatly. All transition states in the assisted aminolysis are 35-70 kJ/mol lower than those for the non-assisted reaction.     

Density functional theory study of calix[4]arene‐N‐azacrown‐5, calix[4]arene‐N‐phenyl‐azacrown‐5, and their complexes with alkali‐metal cations: Na+, K+, and Rb+

Theoretical studies of 1,3‐alternate‐25,27‐bis(1‐methoxyethyl)calix[4]arene‐azacrown‐5 ( L₁ ), 1,3‐alternate‐25,27‐bis(1‐methoxyethyl)calix[4]arene‐N‐phenyl‐azacrown‐5 ( L₂ ), and the corresponding complexes M⁺/ L of L₁ and L₂ with the alkali‐metal cations: Na⁺, K⁺, and Rb⁺ have been performed using density functional theory (DFT) at B3LYP/6‐31G* level. The optimized geometric structures obtained from DFT calculations are used to perform natural bond orbital (NBO) analysis. The two main types of driving force metal–ligand and cation–π interactions are investigated. The results indicate that intermolecular electrostatic interactions are dominant and the electron‐donating oxygen offer lone pair electrons to the contacting RY* (1‐center Rydberg) or LP* (1‐center valence antibond lone pair) orbitals of M⁺ (Na⁺, K⁺, and Rb⁺). What's more, the cation–π interactions between the metal ion and π‐orbitals of the two rotated benzene rings play a minor role. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed in the calix[4]arene molecule. In addition, an extra pendant phenyl group attached to nitrogen can promote metal complexation by 3D encapsulation greatly. In addition, the enthalpies of complexation reaction and hydrated cation exchange reaction had been studied by the calculated thermodynamic data. The calculated results of hydrated cation exchange reaction are in a good agreement with the experimental data for the complexes. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

A One‐Pot Biginelli Synthesis of 6‐Unsubstituted 5‐Aroylpyrimidin‐2(1H)‐ones and 6‐Acetyl‐1,2,4‐triazin‐3(2H)‐ones

The three‐component Biginelli‐like cyclocondensation reaction of enamines 1 , urea, and aldehydes in dioxane/acetic acid efficiently afforded the corresponding 6‐unsubstituted 3,4‐dihydropyrimidin‐2(1H)‐ones 2 in good yields (Scheme 1, Table). The corresponding reaction of azaenamine (=hydrazone) 7 with benzaldehyde and urea afforded 6‐acetyl‐1,2,4‐triazin‐3(2H)‐ones in good yields (Scheme 3).     

(2‐Aminopyrimidine‐κN1)aqua(pyridine‐2,6‐dicarboxylato‐κ3O2,N,O6)copper(II): X‐ray and DFT calculated structure

In the title compound, [Cu(C₇H₃N₂O₄)(C₄H₅N₂)(H₂O)], (I), pyridine‐2,6‐dicarboxylate (pydc²⁻), 2‐aminopyrimidine and aqua ligands coordinate the Cu^II centre through two N atoms, two carboxylate O atoms and one water O atom, respectively, to give a nominally distorted square‐pyramidal coordination geometry, a common arrangement for copper complexes containing the pydc²⁻ ligand. Because of the presence of Cu...X_bridged contacts (X = N or O) between adjacent molecules in the crystal structures of (I) and three analogous previously reported compounds, and the corresponding uncertainty about the effective coordination number of the Cu^II centre, density functional theory (DFT) calculations were used to elucidate the degree of covalency in these contacts. The calculated Wiberg and Mayer bond‐order indices reveal that the Cu...O contact can be considered as a coordination bond, whereas the amine group forming a Cu...N contact is not an effective participant in the coordination environment.     

Specific Intermolecular Interactions in the Supramolecular Structure of 5‐Hydroxy‐6‐Methyluracil: A DFT Study of the Hydrogen‐bonded Dimers

Studying the self‐assembly of uracil derivatives has great importance for biochemistry and nanotechnology. For example, modification of the sorbent surfaces by 5‐hydroxy‐6‐methyluracil (HMU ) enhances their adsorption activity. It is assumed that these changes are caused by the self‐assembly of the network‐like supramolecular associates of the uracil derivative on the sorbent surface. In the present work, the relative stabilities of 15 hydrogen‐bonded dimers HMU have been studied by the TPSSh /TZVP density functional theory method and the strengths of the noncovalent interactions analyzed in terms of the reduced density gradient and natural bond orbital approaches. It was found that the symmetric dimer stabilized by two intermolecular hydrogen bonds N1 –H∙∙∙O–C2 (dimer 1‐1) is the most stable. This suggests that the self‐assembly of HMU should occur through the intermediate formation of the dimer 1‐1. The results may be useful for understanding the processes of self‐assembly of the uracil derivatives and the rationalized design of the uracil‐based supramolecular structures with specific properties.     

Intermolecular interactions of formic acid with benzene: Energy decomposition analyses with ab initio MP2 and double‐hybrid density functional computations

The intermolecular interactions of formic acid (HCOOH) with benzene (C₆H₆) have been investigated using localized molecular orbital energy decomposition analyses (LMO‐EDA) with ab initio MP2 and several double‐hybrid density functionals. The molecular geometries of five HCOOH…C₆H₆ complexes and corresponding benchmark total interaction energies at the CCSD(T)/CBS level are taken from literature (Zhao et al., J. Chem. Theory Comput. 2009, 5, 2726). According to the results of LMO‐EDA with the MP2 method, the dispersion energies are found to be as important as the electrostatic energies for the total interaction energies of the five HCOOH…C₆H₆ complexes. Based on LMO‐EDA with the double‐hybrid density functionals of B2PLYP, B2K‐PLYP, B2T‐PLYP, and B2GP‐PLYP computations, two new parameters for the framework of B2PLYP are extrapolated. These two new parameters are tested with other 10 complexes involving C₆H₆ (Crittenden, J. Phys. Chem. A 2009, 113, 1663), and they perform well on predicting the corresponding total interaction energies. Interestingly, these two new parameters for the framework of B2PLYP also perform well on the noncovalent complexation energies database (NCCE31/05) developed by Truhlar's group (Zhao and Truhlar, J. Phys. Chem. A 2005, 109, 5656). Therefore, these two new parameters appear to be suitable for investigating the noncovalent interactions, and they are denoted as B2N‐PLYP, where N stands for the noncovalent interaction. This study is expected to provide new insight into the derivation of double‐hybrid density functionals for studying the noncovalent interactions. © 2013 Wiley Periodicals, Inc.     

Description of excited states in [Re(Imidazole)(CO)3(Phen)]+ including solvent and spin‐orbit coupling effects: Density functional theory versus multiconfigurational wavefunction approach

The low‐lying electronic excited states of [Re(imidazole)(CO)₃(phen)]⁺ (phen = 1,10‐phenanthroline) ranging between 420 nm and 330 nm have been calculated by means of relativistic spin‐orbit time‐dependent density functional theory (TD‐DFT) and wavefunction approaches (state‐average‐CASSCF/CASPT2). A direct comparison between the theoretical absorption spectra obtained with different methods including SOC and solvent corrections for water points to the difficulties at describing on the same footing the bands generated by metal‐to‐ligand charge transfer (MLCT), intraligand (IL) transition, and ligand‐to‐Ligand‐ charge transfer (LLCT). While TD‐DFT and three‐roots‐state‐average CASSCF (10,10) reproduce rather well the lowest broad MLCT band observed in the experimental spectrum between 420 nm and 330 nm, more flexible wavefunctions enlarged either by the number of roots or by the number of active orbitals and electrons destabilize the MLCT states by introducing IL and LLCT character in the lowest part of the absorption spectrum. © 2016 Wiley Periodicals, Inc.