The influence of universal and specific interactions on structural properties of liquid formamide

Monte Carlo simulation of the structure of liquid formamide at 298 K was carried out. Intermolecular interactions were calculated using five different potentials. No essential changes in the spatial structure and topological properties of the network of hydrogen bonds of liquid formamide occur upon varying the electrostatic intermolecular interactions, strength of H-bonds, and temperature. Fragments of crystal structure are partly retained in liquid formamide. It was found that the network of H-bonds is structurally inhomogeneous and contains long-lived associates of closed cycles of H-bonds as well as tree-like and chain-like structures. The energy, topological, and statistical characteristics of closed cycles of H-bonds were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2227–2236, December, 1999.     

Basis set and electron correlation effects on the polarizability and second hyperpolarizability of model open-shell pi-conjugated systems

The basis set and electron correlation effects on the static polarizability (alpha) and second hyperpolarizability (gamma) are investigated ab initio for two model open-shell pi-conjugated systems, the C(5)H(7) radical and the C(6)H(8) radical cation in their doublet state. Basis set investigations evidence that the linear and nonlinear responses of the radical cation necessitate the use of a less extended basis set than its neutral analog. Indeed, double-zeta-type basis sets supplemented by a set of d polarization functions but no diffuse functions already provide accurate (hyper)polarizabilities for C(6)H(8) whereas diffuse functions are compulsory for C(5)H(7), in particular, p diffuse functions. In addition to the 6-31G(*)+pd basis set, basis sets resulting from removing not necessary diffuse functions from the augmented correlation consistent polarized valence double zeta basis set have been shown to provide (hyper)polarizability values of similar quality as more extended basis sets such as augmented correlation consistent polarized valence triple zeta and doubly augmented correlation consistent polarized valence double zeta. Using the selected atomic basis sets, the (hyper)polarizabilities of these two model compounds are calculated at different levels of approximation in order to assess the impact of including electron correlation. As a function of the method of calculation antiparallel and parallel variations have been demonstrated for alpha and gamma of the two model compounds, respectively. For the polarizability, the unrestricted Hartree-Fock and unrestricted second-order M?ller-Plesset methods bracket the reference value obtained at the unrestricted coupled cluster singles and doubles with a perturbative inclusion of the triples level whereas the projected unrestricted second-order M?ller-Plesset results are in much closer agreement with the unrestricted coupled cluster singles and doubles with a perturbative inclusion of the triples values than the projected unrestricted Hartree-Fock results. Moreover, the differences between the restricted open-shell Hartree-Fock and restricted open-shell second-order M?ller-Plesset methods are small. In what concerns the second hyperpolarizability, the unrestricted Hartree-Fock and unrestricted second-order M?ller-Plesset values remain of similar quality while using spin-projected schemes fails for the charged system but performs nicely for the neutral one. The restricted open-shell schemes, and especially the restricted open-shell second-order M?ller-Plesset method, provide for both compounds gamma values close to the results obtained at the unrestricted coupled cluster level including singles and doubles with a perturbative inclusion of the triples. Thus, to obtain well-converged alpha and gamma values at low-order electron correlation levels, the removal of spin contamination is a necessary but not a sufficient condition. Density-functional theory calculations of alpha and gamma have also been carried out using several exchange-correlation functionals. Those employing hybrid exchange-correlation functionals have been shown to reproduce fairly well the reference coupled cluster polarizability and second hyperpolarizability values. In addition, inclusion of Hartree-Fock exchange is of major importance for determining accurate polarizability whereas for the second hyperpolarizability the gradient corrections are large.     

Carbon blacks as dissipative colloid systems with universal properties

As a new approach the stationary size distribution of particles and aggregates of particles of carbon blacks is described with an extended version of the model of reversible aggregation. Computer simulations of aggregation in dissipative systems lead to ensembles the reduced size distributions of which are at not too short times identical with the universal stationary distribution of the aggregation model. A crucial general point seems to be that structural fluctuations activated by continuously running chemical reactions including viscous dissipation exhibits the same statistics as it is typical for thermally activated aggregation. This leads to the suggestion that the production of carbon blacks at very high temperatures or the reorganization during the so-called CAB-procedure should show a statistically analogous fluctuation-dissipation behaviour as thermally activated aggregation. The ensemble entropy is, in any case, rapidly maximized. In the reactor, for example, a sequence of generations with quasi-stationary ensemble structures is finally built up. Dissipation-fluctuation, including highly cooperative phenomena, guarantees a unique and optimized stationary, thermodynamically “essentially entropy controlled” colloid-structure. Universality is impressively verified by the finding that the particle and aggregate size distributions of different carbon blacks belong to the same “class” so that their reduced representations fall altogether on a master curve. Consequences of our interpretation are discussed. Received: 17 April 2001 Accepted: 1 August 2001     

The effects of geometry on the hyperpolarizability

Extensive studies in the past have focused on precise calculations of the nonlinear-optical susceptibility of thousands of molecules. In this work, we use the broader approach of considering how geometry and symmetry alone play a role, irrespective of molecular constraints. We investigate the nonlinear optical response of potential energy functions that are given by a superposition of force centers (representing the nuclear charges) that lie in various planar geometrical arrangements. We find that for certain specific geometries, such as an octupolarlike molecule with donors and acceptors of varying strengths at the branches, the hyperpolarizability is near the fundamental limit. In these cases, the molecule is observed to be well approximated by a three-level model, consistent with the three-level ansatz previously used to calculate the fundamental limits. However, when the hyperpolarizability is below the apparent limit (about a factor of 30 below the fundamental limit), the system is no longer representable by a three-level model, where both two-level and many-state models are found to be appropriate, depending on the symmetry.     

The effect of electron correlation on the topological and atomic properties of the electron density distributions of molecules

The topological properties of the electron density and the properties of an atom in a molecule are calculated by means of second-order Møller-Plesset perturbation theory (MP2) and compared with the results of configuration interaction calculations (C12) which include all single and double substitutions from the Hartree-Fock reference configuration. A software package for analyzing the effects of electron correlation on the topological properties of the electron density of molecules is described. H₂CO is used to provide a numerical example and to indicate that the number of bond critical points is unaffected by the inclusion of electron correlation. Correlation leads to only a small shift in the positions of bond critical points and a small change in the electron density at bond critical points. It is further shown that the energy of an atom in a molecule can be calculated to an accuracy of 1 kcal/mol and the electron population of an atom to about 0.001e. A statistical method is used to show that the deviation of the MP2 correlation correction relative to the CI2 correlation correction for a variety of atomic properties is about 25%.     

The nitrogen edge-doped effect on the static first hyperpolarizability of the supershort single-walled carbon nanotube

The nitrogen edge-doped effect on the structure, dipole moment, and first hyperpolarizability of the supershort single-walled carbon nanotube (5, 0) has been studied systematically. For the nitrogen edge-doped effect on the structure, the mean diameter on the nitrogen-doped side (D(u)) decreases as the number of doped-nitrogen (n) increases (4.044 (1) > 3.991 (2) > 3.941 (3) > 3.891 (4) > 3.844 A (5)). Significantly, the nitrogen edge-doped effects on the dipole moment and first hyperpolarizability are revealed for the first time and these new effects are dramatic for the supershort single-walled carbon nanotube (5, 0). Among the beta(0) values of these seven nitrogen-doped structures, the largest beta(0) (3155 au) is larger by almost 450 times than the very small beta(0) (7 au) of undoped structure (D(5h)). For nitrogen-doped structures, the order of the beta(0) values is 3155 (1) > 2677 (2A) approximately 2817 (2B) > 1465 (3A) approximately 1458 (3B) > 670 (4) > 254 au (5), which shows two interesting relationships between the beta(0) value and nitrogen-doped number: (1) the smaller the nitrogen-doped number, the larger the beta(0) value. (2) The structures with the same number of doped-nitrogen have almost the same beta(0) values (1465 for 3A and 1458 au for 3B). As for the frequency-dependent beta (-omega; omega, 0) and beta (-2omega; omega, omega), the dependence on the nitrogen-doped number (n) is similar to the case of static beta(0). For beta (-2omega; omega, omega) values at omega = 0.005 au are 3220 (1) > 2720 (2A) approximately = 2862 (2B) > 1480 (3A) approximately = 1477 (3B) > 676 (4) > 256 au (5). In addition, the important monotonic dependences of the beta value on the D(u) and electronic spatial extent are also observed. The new knowledge of influence the beta value will be beneficial to design high-performance nonlinear optical (NLO) materials.     

Three-propeller-blade-shaped electride: remarkable alkali-metal-doped effect on the first hyperpolarizability

Significant alkali-metal-doped effects on the structure and the first hyperpolarizability (β ₀) of effective multi-nitrogen complexant tris[(2-imidazolyl)methyl]amine (TIMA) are investigated. Three imidazoles of TIMA like three blades of propeller connect with methyls by the C–C single bonds. Because of the three C–C single-bond cooperative rotations, the TIMA behaves with great flexibility, and it is a high-performance multi-nitrogen complexant for the alkali metal doping. Thus, the new complexes A_m-TIMA (A_m = Li, Na, and K) with electride characteristic have diffuse excess electron than the reported electride-type system due to the strong interaction between the complexant TIMA and alkali metal. For the first hyperpolarizability, three engaging electrides A_m-TIMA with the diffuse excess electrons exhibit considerably large β ₀ values using the MP2 (full) method and the β ₀ values of new electrides are greatly larger (3,464–29,705 times) than that (338 au) of TIMA. Surprisingly, the K-TIMA sets a new record β ₀ value to be 1.00 × 10⁷ au which far exceeds than that (3,694–76,978 au) of the reported electride-type system Li@calix[4]pyrrole (J Am Chem Soc 127:10977–10981, 2005) and Li_n−H−(CF₂−CH₂)₃−H (n = 1, 2) (J Am Chem Soc 129:2967–2970, 2007) and 31,123 au of the organometallic system (J Am Chem Soc 121:4047–4053, 1999) Ru(trans-4,4′-diethylaminostyryl-2,2′-bipyridine)₃²⁺, as well as 1.23 × 10⁶ au of the large donor-CNT systems (Nano Lett 8:2814–2818, 2008). Clearly, the alkali-metal-doped effect on the first hyperpolarizability is very dramatic for the high-performance multi-nitrogen complexant TIMA. Considering simple possibility from molecule to material, the β ₀ values of optimized Li-TIMA-dimer and Li-TIMA-tetramer are investigated by BHandHLYP method. Interestingly, results show that the order of β ₀ value is Li-TIMA-monomer < Li-TIMA-dimer < Li-TIMA-tetramer. So the new three-propeller-blade-shaped electrides can be considered as candidates for high-performance nonlinear optical materials.     

The effect of interionic interactions on selectivity in uni-bivalent cation exchange systems

Studies of the ion exchange equilibria in the systems potassium-zinc, potassium-cadmium, potassium-cobalt and potassium-nickel, have shown that even at fairly low concentrations (0.1 N) the relative selectivities are affected by the presence of chloride or sulphate ions and that the effects of such ions are more complex than would be deduced from the published data on complex formation in such systems. The implications of these observations on the elution of the bivalent metals from cation exchange columns are briefly discussed.     

The effect of the t-butyl substituent on polymer properties in homopolymer systems

The effect of a bulky substituent on properties of different homopolymers has been examined. The substituent is the t-butyl moiety attached to a benzene ring found in the repeat units of the homopolymers of polyesters, polyarylates, polyamides, and polyaramides. These polymers have been prepared by melt, solution, or interfacial techniques. The source of the t-butyl group is mainly from 5-t-butylisophthalic acid (5TBIA) and comparisons are generally made with corresponding homopolymers based on isophthalic acid. The effect of the t-butyl group is shown by comparison of the properties of these homopolymers. Thermal and mechanical (tensile and impact) properties, density, water absorption, solubility, and processability are discussed. Differences in these properties are attributed to the t-butyl group and are based on intermolecular and intramolecular interactions that include increased free volume, chain stiffening, and conformational changes.     

The effect of inertia on the intrinsic viscosity of polymers

For the model of an elastic dumbbell, i.e., two beads connected by a Hookean spring, the Langevin equations for the beads are formulated. It is taken into account that the friction force contains terms resulting from the inertia of the liquid. The contribution of the dumbbell to the viscosity is calculated from the rate of energy dissipation. When the inertia of the liquid is neglected, the viscosity contribution reduces to Kramers' result and is independent of the mass of the beads. When the inertia terms are added, the result is nearly independent of this mass, but shows a dependence on the density of the liquid. In liquids of low viscosity, the extra term resulting from the inertia may be as large as 25% of the total viscosity contribution.     

The effect of electron detachment on the structure and properties of the chlorine-acetonitrile anionic complex

The results of the theoretical study of ground state potential energy surfaces for the chlorine-acetonitrile anion and its photodetachment product are presented. The shallow potential surfaces allow for the nondefinitive position of the chlorine within the complex. The dissociation energy of the neutral complex, estimated through the thermodynamic cycle, indicates significant structural changes due to the photodetachment process. The excess negative charge is localized mostly on the chlorine atom, and the electron detachment proceeds as an electron is removed from chlorine. The process leads to drastic changes in the electrostatic interactions within the complex. The first electronic excited state corresponds to the excess electron transfer from chlorine to acetonitrile fragment. This state is a precursor of the observed charge-transfer-to-solvent state.     

最优特征子集预测蛋白质与蛋白质的相互作用

蛋白质与蛋白质相互作用的识别有助于研究蛋白质功能和发现潜在的药物靶标。本研究采用氨基酸组成、二肽组成、三联子组成、组成、转变、分布和自相关特征对蛋白质与蛋白质相互作用对进行表征。基于最小冗余最大相关方法选择最优特征子集,结合支持向量机对酵母蛋白质与蛋白质相互作用进行了预测研究。通过采用最优特征子集,训练集和测试集的预测精度分别比二肽组成的提高了4%和2%,表明了当前方法的有效性。     

Origin of the enhancement of the second hyperpolarizability of singlet diradical systems with intermediate diradical character

The origin of the diradical character dependence of the second hyperpolarizability (gamma) of neutral singlet diradical systems is clarified based on the perturbation formula of gamma using the simplest diradical molecular model with different diradical characters, i.e., H2 under bond dissociation. The enhancement of gamma in the intermediate diradical character region turns out to originate from the increasing magnitude of the transition moment between the first and second excited states and the decrease of that between the ground and first excited states, respectively, with the increase in diradical character. This feature confirms that open-shell singlet conjugated molecules with intermediate diradical characters constitute a new class of third-order nonlinear optical systems, whose gamma values can be controlled by the diradical character in addition to the conjugation length.     

Electronegative oligothiophenes fully annelated with hexafluorocyclopentene: synthesis, properties, and intrinsic electron mobility

Synthesis of hexafluorocyclopenta[c]thiophene-repeated oligothiophenes up to 6-mer has been accomplished. The photophysical and electrochemical properties of these oligomers unambiguously exemplify marked electronegative character without disrupting the effective conjugation. The combination of time-resolved microwave conductivity and transient optical spectroscopy measurements of the 6-mer revealed the intrinsic electron mobility to be as high as 2.0 x 10(-1) cm(2) V(-1) s(-1).     

Dynamic hyperpolarizability calculations of large systems: the linear-scaling divide-and-conquer approach

We report a linear-scaling computation method for evaluating the dynamic first hyperpolarizability β based on the divide-and-conquer (DC) method. In the present scheme, we utilized the quasi-density-matrix expression derived from Wigner's (2n + 1) rule for β, where the quasi-density matrices are constructed from the solution obtained via the DC time-dependent self-consistent field (TD-SCF) method [T. Touma, M. Kobayashi, and H. Nakai, Chem. Phys. Lett. 485, 247 (2010)]. Numerical evaluation of π-conjugated and saturated organic chain systems verified that the present scheme considerably reduces the computational time for the β evaluation with a slight loss of accuracy, even around the singular frequency appearing at the electronic excitation energy. This evaluation indicates that the present linear-scaling TD-SCF scheme can also be used to estimate the molecular excitation energy. Furthermore, we succeeded in accurately evaluating the macroscopic second-harmonic generation coefficient of the polyvinylidene fluoride from the molecular (hyper)polarizabilities.     

The influence of intermolecular interactions in n-pentane-alkane-1-ol systems on their physicochemical properties

The Helmholtz energy of dipole-dipole interaction (ΣΔ_d F) and its long-range (Δ_d F°) and short-range (Δ_d F*) components were calculated for n-pentane-alkane-1-ol (from methanol to dodecane-1-ol) systems at 298.15 K using the Winkelmann statistical model theory of liquid dielectrics. It was shown that the longer the alkane-1-ol hydrocarbon radical, the greater the extent to which the properties of the systems with n-pentane were determined by the structure of n-alkane.     

Assessment of the intrinsic interactions of mesoporous silica with carbon dioxide

Three mesoporous silica, SBA-16, SBA-15 and MCM-41, with different structures and porosities were synthesized via a hydrothermal method and their interactions with carbon dioxide (CO₂) were investigated through thermal programmed desorption (TPD) and differential scanning calorimetry. TPD measurements provided precise assessments of the intrinsic affinity towards CO₂, without the influence of moisture. All silica materials were found to exhibit intrinsic affinity towards carbon dioxide, but the surface basicity, expressed in terms of retained CO₂ amount, is markedly influenced by increases in pore size and framework structures. SBA-15 displayed the highest CRC values, explained in terms of larger pore size, lower numbers of acidic out-of plane Si–OH and higher numbers of much less acidic in-plane silanols. These findings provide valuable information for a better understanding of the role of the silica structure in the intrinsic basicity, prior to further modifications for improving the affinity towards CO₂ or merely for catalysis purposes involving CO₂ as reagents, intermediates or products.     

取代基对醌的结构及电子转移能力的影响

用半经验的AM1,abinitio(HF/3-21G,HF/6-31G^*),及密度泛函[B3LYP/6-31G^*,B3LYP/6-311G(d,p)]方法对1,4-苯酯及其阴离子的结构与性质进行了研究。在此基础上用AM1及BLYP/6-31G(d,p)方法对泛醌Q~0,用AM1方法对泛醌Q~1,泛醌Q~2及其阴离子的结构与性质进行了研究。研究结果表明,由于取代基的影响,泛醌的环平面发生了扭曲,环上原子不再位于同一平面上。结构的变化导致了电子分布发生了变化,并由此导致了偶极矩随6位上取代基的增大而增大。随着6位支链的增长,泛醌的电离势逐渐减小而电子亲和势逐渐增大,泛醌传递电子的能力增强。在上述研究的基础上,对1,4-苯醌及泛醌的自交换电子转移反应过程进行了过程,计算了反应的内重组能,溶剂重组能及电子转移速率常数。结果表明内重组能的大小与取代基的长短无直接关系,而与得电子前后醌的结构变化程度密切相关。除高频振动的变化外,低频振动的变化对内重组能也有显著的贡献。计算所得1,4-苯醌自交换电子转移反应速率常数与实验值相符得很好。     

Fully optimized implementation of the cluster-in-molecule local correlation approach for electron correlation calculations of large systems

A fully optimized implementation of the cluster-in-molecule (CIM) local correlation method for faster and more accurate electron correlation calculations of large systems is reported. The speedup comes from the new procedure of constructing virtual localized molecular orbitals of clusters. In the new procedure, Boughton–Pulay projection method is employed instead of a much more expensive Boys localization procedure. In addition, basis set superposition error correction for binding energy calculations and parallelized electron correlation calculations of clusters are now implemented. Benchmark calculations and illustrative applications at the Møller–Plesset perturbation theory, coupled cluster singles and doubles (CCSD), and CCSD with perturbative triples correction levels show that this newly optimized CIM approach is a reliable theoretical tool for electron correlation calculations of various large chemical systems. © 2018 Wiley Periodicals, Inc.     

Giant electric field effect on the second hyperpolarizability of symmetric singlet diradical molecules

This contribution reveals the effects of a static electric field on the static second hyperpolarizability γ of symmetric singlet diradical molecules using the valence configuration interaction scheme. It is found that under the effect of a field, the component of γ along the axis joining the two radical sites can be gigantically (approximately two to three orders) enhanced for symmetric diradicals having intermediate diradical characters with respect to those of closed-shell and pure diradical molecules in the absence of a field. Moreover, this electric field enhancement of γ increases as a function of the diradical character. These results and their analysis propose therefore a new strategy to design materials with exceptional nonlinear optical responses.