Structural stability analysis of Wigner crystal with Gaussian and Yukawa‐type positive background

Calculations of the ground‐state energies of Wigner crystals having simple cubic (sc), body‐centered cubic (bcc), face‐centered cubic (fcc), diamond, and perovskite structures and (hence) the analysis of relative stability of Wigner crystals of various different structures are reported. The positive background is represented by a periodic array of Gaussians and Yukawa‐type distribution. The effects on stability of the perturbation due to the underlying lattice have been demonstrated. Among the structures, the bcc lattice still remains the most stable known arrangement and the Yukawa‐type background leads to a lower ground state energy value compared to a Gaussian type. The calculations are done for the range of the density parameter r_s corresponding to low densities for the above two cases. The range of low‐density region favorable for Wigner crystallization is found to be above r_s=20. The role of correlation energy is suitably taken into account. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Trapping of photogenerated group IV radicals by TEMPO: Potential new organometallic initiators for “living” free radical polymerization

A series of trialkyl and triaryl organometallic radicals from group IV generated by hydrogen abstraction by tert‐butoxyl radical from the parent hydrides have been examined using laser flash photolysis. The rate constants for the trapping of the metal‐centered radicals by the persistent radical TEMPO were measured and were found to be large and similar to those of the carbon‐centered radical systems, yet below the diffusion controlled limit. The metal‐centered radicals were found to be efficiently trapped by TEMPO and would appear to be candidates suitable for “living” free radical polymerization similar to carbon analogue stoichiometric initiators. The radical trapping rate constants for the trialkyl series (M = Si, Ge, Sn) were found to be 8.9 × 10⁸ M⁻¹ s⁻¹ (M = Si), 7.2 × 10⁸ M⁻¹ s⁻¹ (M = Ge), and 6.2 × 10⁸ M⁻¹ s⁻¹ (M = Sn), respectively. The triaryl (Ph₃M•) series gave slightly slower rates of 1.6 × 10⁸ M⁻¹ s⁻¹ (M = Si), 3.4 × 10⁸ M⁻¹ s⁻¹ (M = Ge), and 1.9 × 10⁷ M⁻¹ s⁻¹ (M = Sn), respectively. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 238–244, 2000     

Molecular DFT structure and packing effect of thiodipropionic and dithiodiglycolic acids and salts

Molecular and periodic DFT structure calculations of thiodipropionic and dithiodiglycolic acids, S_n[(CH₂)(COOR)]₂ (n = 1,2, R = H, Na), were performed. Computed structures were analyzed and compared to the experimental data (a C_s conformation is favored in solution than C₂ in solid state). Four close and low-energy optimized conformations were analyzed: C_2v, C₂, C_s and C₁. Small changes in the conformation stability (ΔG) and symmetry group were observed in polar medium. Periodic DFT-GGA approaches have been performed to determine the importance of weak interaction upon the crystal structure of the thiodipropionic acid, e.g., S–H and/or O–H hydrogen bonding. More SH and OH dispersed bands were observed in the optimized structure. Using a full analysis of the DOS of O–H or S–H bonding contributions, a notable interlayer bonding in the parent structure was revealed. Therefore, the presence of such weak interaction ONa⁺ or OH may thus change the point group symmetry of the crystal upon packing effect.     

Modified Gaussian functions and their use in quantum chemistry. I. Integrals

A modified Gaussian function g(u, v, w, a, R ) = const s(a, R ) is considered where l = u + v + w, s (a, R ) is a 1s-type Gaussian function centered at R , a is the coefficient in the exponent of the 1 s Gaussian function and X, Y, Z are components of R . General formulae are derived for overlap integrals, kinetic energy integrals, nuclear attraction integrals, and electron repulsion integrals, valid for any l. The formulae are much simpler than those derived by Huzinaga for Cartesian Gaussian functions.     

Alignment of Heptagonal Diimide and Triazine Enables Narrowband Pure-Blue Organic Light-Emitting Diodes with Low Efficiency Roll-Off

The endeavor to develop high-performance narrowband blue organic light-emitting diodes (OLEDs) with low efficiency roll-off represents an attractive challenge. Herein, we introduce a hetero-acceptor design strategy centered around the heptagonal diimide (BPI) building block to create an efficient thermally activated delayed fluorescence (TADF) sensitizer. The alignment of a twisted BPI unit and a planar diphenyltriazine (TRZ) fragment imparts remarkable exciton dynamic properties to 26tCz-TRZBPI, including a fast radiative decay rate (k_R) of 1.0×10⁷ s⁻¹ and a swift reverse intersystem crossing rate (k_RISC) of 1.8×10⁶ s⁻¹, complemented by a slow non-radiative decay rate (k_NR) of 6.0×10³ s⁻¹. Consequently, 26tCz-TRZBPI facilitates the fabrication of high-performance narrowband pure-blue TADF-sensitized fluorescence OLEDs (TSF-OLEDs) with a maximum external quantum efficiency (EQE_max) of 24.3 % and low efficiency roll-off even at a high brightness level of 10000 cd m⁻² (EQE₁₀₀₀₀: 16.8 %). This showcases a record-breaking external quantum efficiency at a high luminance level of 10000 cd m⁻² for narrowband blue TSF-OLEDs.     

Divinylketone: Conformational preferences. Molecular geometry and vibrational force field in the ground state

The conformational preferences of the molecule 1,4-pentadien-3-one (divinylketone) have been studied by ab initio molecular orbital calculations and discussed in terms of interaction between molecular fragments. The calculations predict a molecular ground state having a fully coplanar s-cis, s-cis conformation. In addition, we find three other structures that represent local minima on the energy surface. These are a fully coplanar s-cis, s-trans form, and two nonplanar s-trans, s-trans forms having symmetries C₂ and C_1h, respectively. The energies of these forms relative to the ground state are 7.5, 19.2, and 35.9 kJ/mol, respectively. The coplanar s-trans, s-trans form represents a saddle point on the energy surface. All conformers and the saddle point have been completely geometry optimized by the gradient technique. For the ground state a complete in-plane harmonic force field has been evaluated.     

STUDY ON LIGHTLY SULFONATED SYNDIOTACTIC POLYSTYRENE IONOMERS

Sulfonated syndiotactic polystyrene ionomers (SsPS) with 1.8 mol% degree of sulfonation have been studied.WAXD shows that the crystallinity of SsPS ionomers was decreased with increasing diameter size of the counter ions andsPS>SsPS-H>SsPS-K>SsPS-Zn. Moreover, SsPS ionomers only have a α cystal form, while original sPS has two crystalforms: α and β crystal form. TGA shows that the thermal stability of SsPS ionomers is higher than that of the original sPSand SsPS-Zn>SsPS-K>SsPS-H. DSC shows that all the glass transition temperatures (T_g) of SsPS ionomers are higherthan that of the neat sPS and SsPS-Zn>SsPS-Na>SsPS-K>SsPS-H. However, the melting temperature (T_m) andcrystallization peak temperature (T_p) of SsPS ionomers are lower and SsPS-H>SsPS-Zn>SsPS-K>SsPS-Na, while thecrystallinity (X_c) of SsPS-Zn is the lowest. Nonisothermal crystallization kinetics shows that the Avrami index of sPS andSsPS-H are both about 4, suggesting the nucleation growth of SsPS-H with lower degree of sulfonation still keeps its three-dimension form. FTIR spectra of SsPS ionomers show a splitting absorption band for asymmetric stretching vibration ofsulfonation group. The CH in-plane bending vibration of benzene ring shifted to higher wavenumber and the symmetricstretching vibration of sulfonation group changed slightly with different counter ion neutralized SsPS ionomers.     

Relativistic calculation of autoionization widths of 1s2s2pjJ, 1s2s2 2S1/2, and 1s2pJ 2pj′J levels

The autoionization widths of levels 1s 2s 2p_jJ, 1s2s^{2 2}S_1/2, and 1s2p_j2p_j′ J have been calculated for ions with Z = 6–30. The calculation has been carried out in intermediate coupling. The decay amplitudes have been calculated in a relativistic approximation.     

Intrinsic Rate Constants ket of Photoinduced Electron Transfer between Anthracene Derivatives and Aromatic Donors: Does the Intersecting‐State Model Challenge Marcus Theory When Confronted with an Archetypal Set of Data?

Intrinsic photoinduced electron transfer (PET) rate constants k_et, resorting to classically studied acceptor‐donor couples, are confronted to two theoretical models of electron transfer. At a very exergonic driving force, k_et remains on a plateau value centered around 10¹¹ s⁻¹. It is shown that the well‐known and widely used Marcus theory fails to account for the data located on this plateau. On the contrary, the basically different approach of the intersecting‐state model (ISM) allows fitting the whole set of data with physically realistic parameters. The possibility is discussed that this success of the ISM over the Marcus model may give hints to explain the lack of an inverted region in forward PET in solution.     

Antiferromagnetic phase of a 2‐D Wigner crystal

The antiferromagnetic phase of a 2‐D Wigner crystal is investigated, using a localized representation for electrons. In our model, the electrons are located at the lattice sites of a face‐centered square lattice (corresponding to bcc in the 3‐D case). This lattice may be thought of as consisting of two equivalent interpenetrating sublattices. The ground‐state energies of the antiferromagnetic phase of a 2‐D Wigner electron crystal are computed with uniform neutralizing, Gaussian‐type, and Yukawa‐type positive backgrounds in the range of r_s = 5 to 130. The role of correlation energy is suitably taken into account. The possibility of the antiferromagnetic phase of the 2‐D Wigner crystal having a square or circle as the region of occupation in momentum space is also analyzed. The low‐density region favorable for the antiferromagnetic phase of Wigner crystallization is found to be at r_s = 7.0. Our results agree well with experimental and other theoretical results for the 2‐D Wigner crystal. The structure‐dependent Wannier functions, which give proper localized representation for Wigner electrons, are constructed and employed in the calculation for the first time. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Poly[(μ4‐adamantane‐1,3‐dicarboxylato‐κ5O1:O1′:O3,O3′:O3′)(μ3‐adamantane‐1,3‐dicarboxylato‐κ5O1,O1′:O3,O3′:O3′)dimagnesium]: a layered coordination polymer

The title compound, [Mg₂(C₁₂H₁₄O₄)₂]_n, is the first example of an s‐block metal adamantanedicarboxylate coordination polymer. The asymmetric unit comprises two crystallographically unique Mg^II centers and two adamantane‐1,3‐dicarboxylate ligands. The compound is constructed from a combination of chains of corner‐sharing magnesium‐centered polyhedra, parallel to the a axis, connected by organic linkers to form a layered polymer. The two Mg^II centers are present in distorted tetrahedral and octahedral coordination environments derived from carboxylate O atoms. Tetrahedrally coordinated Mg^II centers have been reported in organometallic compounds, but this is the first time that such coordination has been observed in a magnesium‐based coordination polymer. The bond valance sums of the two Mg^II centers are 2.05 and 2.11 valence units, matching well with the expected value of 2.     

1/Z perturbation theory for calculation of line strengths in the neon isoelectronic sequence

The line strengths of 2–2 and 3–3 transitions (2s²2p⁵3s–2s²2p⁵3p–2s²2p⁵3d, 2s2s2p⁶3s–2s2p⁶3p-2s2p⁶3d, 2s²2p⁵3l-2s2p⁶3l) have been calculated for the Ne isoelectronic sequence (Z = 14 ÷ 100). The calculation has been carried out in intermediate coupling. Relativistic corrections have been included through the Breit operator. Perturbation theory in 1/Z has been used to account for electronic interactions.     

Bound states of helium atom in dense plasmas

We have obtained the bound 1s^{2 1}S, 1s2s ^1,3S, and 1s2p ^1,3P states energies of helium atom in dense plasma environments in accurate variation calculations. A screened Coulomb potential to represent the Debye model is used for the interaction between the charged particles. A correlated wave function consisting of a generalized exponential expansion has been used to take care of the correlation effect. The 1s^{2 1}S, 1s2s ^1,3S, and 1s2p ^1,3P states energies along with the ionization potential, the energy splitting between the 1s2s ³S, and 1s2s ¹S states, transition energies between the ground state and low‐excited states of He estimated for various Debye lengths, are reported. The results show high degree of accuracy even under strong plasma conditions. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

A theoretical investigation of the singly excited two-electron atomic states 1s2s3S and 1s3s3S

The singly-excited two-electron states 1s2s ³S and ls3s ³S have been investigated by means of the variational perturbation theory procedure. The wave functions have been constructed as linear combinations of Hylleraas terms with hyperbolic factors in t, and the results obtained by carrying the computations through to 10th perturbation order and with 36(37)- 57(58)- and 85(86)-term basic sets, respectively, are reported. These results compare favourably with the corresponding best values from previous conventional variational calculations.     

Micellar Exchange Kinetics of Quaternary Ammonium Type Gemini Surfactants Monitored by Nuclear Magnetic Resonance

The dynamic NMR (DNMR) method was used to detect kinetic parameters of the molecular exchange process between monomers in bulk solution and those in the micelle for Gemini surfactants, 12-s-12 and 14-s-14(s=2, 3 and 4).The escape rate constant, k^-, was derived based on the simplified equations of DNMR theory, and the apparent activation energy of escape, E_a^-, was obtained based on the Arrhenius equation through temperature variation experiments.Results show that the orders of magnitude of k^- for 14-s-14 and 12-s-12 are respectively 10 and 10³ s^-1, E_a^- of 14-s-14 and 12-s-12 are respectively 54.04-73.64 and 33.42-47.09 kJ/mol.Furthermore, increases and E_a^- decreases with the spacer length growing.In combination with the micro-polarity measurements, it was revealed that molecules of 14-s-14 and 12-s-12 have to experience conformation changes when escaping from the micelles.The two-step molecular exchange mechanism for Gemini surfactants was therefore supported.     

Compact contracted basis sets for third-row atoms: Ga–Kr

The (14s11p5d) primitive basis set of Dunning for the third-row main group atoms Ga-Kr has been contracted [6s4p1d]. The core functions have been relatively highly contracted while those which represent the valence region have been left uncontracted to maintain flexibility. Calculations with the [6s4p1d] contraction are reported for a variety of molecules involving third-row atoms. This basis set is found to satisfactorily reproduce experimental properties such as geometric configurations, dipole moments, and vibrational frequencies for a range of molecules. Comparisons are made with the performance of the uncontracted basis set. Polarization functions for the contracted basis set are reported and performance of the basis set with and without polarization functions is examined. A relaxation of the [6s4p1d] contraction to [9s6p2d] for higher level evergy calculations is also presented.     

Synthesis and properties of polyurethanes containing s-triazine rings in the main chain

Eight new diisocyanate monomers containing s-triazine ring have been prepared from the parent diacids via the Curtius rearrangement of the corresponding diacyl azides. The parent diacids were synthesised by the reaction of p- and m-hydroxybenzoic acid with 6-methoxy-2,4-dichloro-s-triazine, 6-phenoxy-2,4-dichloro-s-triazine, 6-phenyl-2,4-dichloro-s-triazine, and 2-diphenylamino-4,6-dichloro-s-triazine respectively. Polyurethanes have been synthesised by solution polymerization of these diisocyanates with ethylene glycol in N,N-dimethylacetamide (DMAC). The resulting polymers were characterized by IR spectroscopy, viscosity measurement, solubility tests, and softening points.     

Evaluation method of steric shielding effect around nitroxide radical reaction center based on molecular volume within a virtual ball

Steric shielding affects the stability of various molecules such as nitroxide radicals, which have many applications in a variety of fields. Thus, the mechanisms that maintain molecular stability are of particular interest. A new method for nitroxide radicals to quantify the steric shielding effect around the reaction center in a molecule was developed. The steric hindrance in this method is defined as the volume of the molecules contained within a virtual ball centered on the radical atom. With the proposed method, it is possible to evaluate the influences of the β-substituent, the basic molecular skeleton, and other parameters on steric hindrance, which cannot be calculated with E_s^c, a known parameter that indicates bulkiness. This method can acquire more accurate data that more closely resembles the behavior of the actual molecule. Because this method is very simple in that it requires only the optimal stable structure of the molecule, it can be used to estimate the steric shielding of various nitroxide radicals as well as other molecules.

     

Basis set quality versus size II. Approximate GTO wave functions for second row transition metal atoms

Basis sets ranging in size from (16, 10, 7) to (20, 14, 11) have been derived for the atoms Y–Cd. Separate sets represent the energy optimized wave functions for each of the s²dⁿ, s¹dⁿ⁺¹, and s⁰dⁿ⁺² configurations. The energies from the largest sets are within 3 mhartrees of the values obtained in numerical Hartree–Fock calculations. Reasonable Hartree–Fock s²dⁿ– s¹dⁿ⁺¹ and s²dⁿ– s⁰dⁿ⁺² excitation energies may be obtained either using the largest basis sets, or using d-orbitals optimized for the s⁰dⁿ⁺² configurations. The basis sets are slightly unbalanced in favor of the s-functions and in disfavor of the d-functions, but various alternative basis sets may be derived by combining parts of the five parent sets. The convergence of radial expectation values is discussed.