Universal Algorithm for Reconstruction of Atomic Models of Noncrystalline Systems

A new algorithm is suggested for constructing models of noncrystalline substances from a known pair correlation function (PCF). The algorithm allows the models to be reconstructed for any temperature, including the vicinity of absolute zero. The algorithm compares the coordination numbers of the target and model PCFs for all distances of the PCF histogram. The coordination number comparison algorithm includes calculating, in each iteration, a correction to the pair force function and ensures the convergence of the process to the sought force function at which the PCF of the molecular dynamic (or static) model practically coincides with the target PCF. The algorithm makes it possible to attain a very small standard deviation of the model PCF from the target PCF (~0.01) at which the plots of the two functions are visually indistinguishable. Reconstructed force functions usually differ from the functions used in the construction of target models. This indicates nonuniqueness of the solution of the inverse problem of modeling.     

Thermodynamics of sublimation,thermophysical and structural aspects of the molecular crystals of fenamates

A method of transfer with an inert carrier gas is used to obtain temperature dependences of pressure vapors. The thermodynamic functions of sublimation processes are calculated for seven molecular crystals that belong to the group of non-steroidal anti-inflammatory drugs: diclofenac, niflumic, flufenamic, tolfenamic, mefenamic, N-phenylanthranilic acids, and diphenylamine. Differential scanning calorimetry is applied to study the melting processes of the selected substances. Single crystal X-ray structural literature data are analyzed, and they are compared with the obtained thermodynamic and thermophysical parameters of sublimation and melting processes. A correlation between the values of the enthalpy of sublimation and the melting temperature under standard conditions is found. The effect of different substituents on the crystal lattice energy of this class of compounds is studied.     

On linear programming approach for the calculation of chemical equilibrium in complex thermodynamic systems

The advantages of linear programming approach for the calculation of chemical equilibrium in complex thermodynamic systems are demonstrated. The algorithm presented is used for the development of software package for thermodynamic modeling.     

The use of the terms formal element,initial and detailed components,and phase and chemical form in modeling of the states of homo- and heterogeneous systems

The terms formal element, initial and detailed components, and phase and chemical form and their use in chemical thermodynamic modeling of the state of substances in homo- and heterogeneous systems with taking into account local and partial equilibria are considered. The detailed component concept is introduced into fundamental equations. The use of the concept of formal elements is illustrated.     

The Soave,Twu and Boston–Mathias alpha functions in cubic equations of state: Part I. Theoretical analysis of their variations according to temperature

A theoretical analysis of the strengths and weaknesses of the Soave, Twu and Boston–Mathias attractive terms was performed with the Redlich–Kwong EoS. Special attention was paid to the variations of the alpha functions and their first and second derivatives with respect to temperature. Contrary to the Soave function, abnormal behaviors of the derived Twu and Boston–Mathias functions were evidenced in the temperature range commonly covered by industrial applications. The unsuccessful variations of the derived alpha functions observed with these two last models strengthen the interest of the Soave equation for the modeling of derived thermodynamic properties. The accuracy of pure component data modeling by means of the cubic equation of state is discussed in a second part.     

近代低温绝热量热学的研究现状及发展前景

低温绝热量热法是化学热力学研究领域中重要的实验方法之一。由此方法所获得的许多结果,如宽温区摩尔热容、标准熵、标准热力学函数、相变温度、相变焓、相变熵、相变机理以及与物质结构和能量相关的许多其它重要信息,对各种物质或材料的理论研究和应用开发具有重要的指导作用。为此,本文对低温绝热量热法的研究意义、仪器发展概况和趋势、国内外研究现状、应用前景及研究课题展望等作了较为详细的评述。     

Novel bare-bones particle swarm optimization and its performance for modeling vapor-liquid equilibrium data

Parameter estimation in models plays a significant role in developing mathematical models which are used for understanding and analyzing physical, chemical and biological systems. Parameter estimation problems for vapor-liquid equilibrium (VLE) data modeling are very challenging due to the high non-linearity of thermodynamic models. Recently, stochastic global optimizations and their applications to these problems have attracted greater interest. Of the many stochastic global optimization methods, Bare-bones particle swarm optimization (BBPSO) is attractive since it has no parameters to be tuned by the user. In this study, modifications are introduced to the original BBPSO using mutation and crossover operators of differential evolution algorithm to update certain particles in the population. The performance of the resulting algorithm is tested on 10 benchmark functions and applied to 16 VLE problems. The performance of the proposed BBPSO for VLE modeling is compared with that of other stochastic algorithms, namely, differential evolution (DE), DE with tabu list, genetic algorithm and simulated annealing in order to identify their relative strengths for VLE data modeling. The proposed BBPSO is shown to be better than or comparable to the other stochastic global optimization algorithms tested for parameter estimation in modeling VLE data.     

Heat capacity and thermodynamic functions of 4,4′-dimethylbiphenyl and 4,4′-di-tert-butylbiphenyl

The heat capacity (C _{p m} ) of 4,4′-dimethylbiphenyl and 4,4′-di-tert-butylbiphenyl in the temperature range of 8—373 K was measured by low-temperat ure adiabatic calorimetry, and thermodynamic characteristics of the solid-phase transitions of 4,4′-d i-tert-butylbiphenyl were determined. Temperatures, enthalpies, entropies of melting, and the purity of the samples of the tested substances were determined by means of differential scanning calorimetry. The main thermodynamic functions of the substances in the condensed state at 298 K were calculated.     

Prediction of peptide conformation by multicanonical algorithm: New approach to the multiple-minima problem

We apply a recently developed method, the multicanonical algorithm, to the problem of tertiary structure prediction of peptides and proteins. As a simple example to test the effectiveness of the algorithm, metenkephalin is studied and the ergodicity problem, or multiple-minima problem, is shown to be overcome by this algorithm. The lowest-energy conformation obtained agrees with that determined by other efficient methods such as Monte Carlo simulated annealing. The superiority of the present method to simulated annealing lies in the fact that the relationship to the canonical ensemble remains exactly controlled. Once the multicanonical parameters are determined, only one simulation run is necessary to obtain the lowest-energy conformation and further the results of this one run can be used to calculate various thermodynamic quantities at any temperature. The latter point is demonstrated by the calculation of the average potential energy and specific heat as functions of temperature. © John Wiley & Sons, Inc.     

Thermodynamics and molecular dynamics of some ferrocene derivatives

The heat capacities of acetylferrocene, 1,1′-diacetylferrocene, and 1,1′-diethylferrocene were investigated by low-temperature adiabatic calorimetry in the temperature range from 5 to 300 K and their thermodynamic functions were calculated. The enthalpies of combustion of the substances were determined by calorimetry of combustion, and the thermodynamic functions of their formation were calculated by quantum chemistry methods. Inter- and intramolecular interactions of the ferrocene derivatives were also studied by the methods of molecular mechanics and molecular dynamics. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1668–1676, September, 1999.     

水-乙醇二元体系共沸混合物的热力学研究

用全自动低温绝热量热计测定了水、乙醇以及水和乙醇组成的共沸混合物在不同温区的摩尔热容Cp,m. 建立了共沸混合物Cp,m与温度T的函数关系.结果表明,水和乙醇组成的共沸混合物在98.496 K发生玻璃态转化,在158.939 K 和270.95 K发生固-液相变.获得了其相应的相变焓和相变熵.计算了以298.15 K为基准的该共沸混合物的热力学函数和超额热力学函数.     

Integrated experimental-theoretical investigation of the Na-Li-Al-H system

First-principles modeling, experimental, and thermodynamic methodologies were integrated to facilitate a fundamentally guided investigation of quaternary complex hydride compounds within the bialkali Na-Li-Al-H hydrogen storage system. The integrated approach has broad utility for the discovery, understanding, and optimization of solid-state chemical systems. Density functional theory ground-state minimizations, low-temperature powder neutron diffraction, and low-temperature synchrotron X-ray diffraction were coupled to refine the crystallographic structures for various low-temperature distorted Na2LiAlH6 allotropes. Direct method lattice dynamics were used to identify a stable Na2LiAlH6 allotrope for thermodynamic property predictions. The results were interpreted to propose transformation pathways between this allotrope and the less stable cubic allotrope observed at room temperature. The calculated bialkali dissociation pressure relationships were compared with those determined from pressure-composition-isotherm experiments to validate the predicted thermodynamic properties. These predictions enabled computational thermodynamic modeling of Na2LiAlH6 and competing lower order phases within the Na-Li-Al-H system over a wide of temperature and pressure conditions. The predictions were substantiated by experimental observations of varying Na2LiAlH6 dehydrogenation behavior with temperature. The modeling was used to identify the most favorable reaction pathways and equilibrium products for H discharge/recharge in the Na-Li-Al-H system, and to design conditions that maximize the theoretical hydrogen reversibility within the Na-Li-Al-H system.     

Thermodynamic properties of the binary mixture of water and <Emphasis Type="Italic">n</Emphasis>-butanol

The molar heat capacities of the binary mixture composed of water and n-butanol were measured with an adiabatic calorimeter in the temperature range 78–320 K. The functions of the heat capacity with respect to thermodynamic temperature were established. A glass transition, solid–solid phase transition and solid–liquid phase transition were observed. The corresponding enthalpy and entropy of the solid–liquid phase transition were calculated, respectively. The thermodynamic functions relative to a temperature of 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature.     

Thermodynamics of alternating copolymer of styrene and CO in the 0—600 K region

The temperature dependence of heat capacity and the temperatures and enthalpies of physical transitions of the alternating copolymer of styrene and CO were studied in the 5—600 K region by the adiabatic vacuum and dynamic calorimetric techniques. The heat of combustion of the copolymer was measured at 298.15 K in a calorimeter with a static bomb and an isothermal shield. The thermodynamic parameters of glass transition and fusion were determined. The thermodynamic functions in the 0—550 K region and thermodynamic characteristics of the formation of the copolymer from simple substances at T = 298.15 K and p = 101.325 kPa were calculated. The thermodynamic parameters of alternating copolymerization in the bulk of styrene and CO were calculated in the 0—350 K region at a standard pressure.     

Thermodynamic properties of cerium mononitride

Data on the thermodynamic properties of cerium mononitride CeN in the solid state are analyzed. Relations approximating the temperature dependence of the thermodynamic functions of CeN(cr.) in the temperature range of 298.15–2900 K are obtained. Using the relations of thermodynamics known for this temperature range, the thermodynamic functions of cerium mononitride (entropy, Gibbs energy, and enthalpy variation) are calculated. The resulting data is entered into the database of the IVTANTHERMO software package and is used to analyze the thermal stability of CeN(cr.), and to estimate its boiling point at atmospheric pressure.     

The heat capacity of titanium di-and tetrachloride over the temperature range 7-314 K

The temperature dependences of the heat capacities of titanium di-and tetrachloride were studied by vacuum adiabatic calorimetry. The parameters of fusion (T _tr, Δ_tr H, and Δ_tr S) were determined for TiCl₄. The thermodynamic functions of the substances were calculated over the temperature range 10–300 K. The results obtained were compared with literature data.     

Thermodynamics of alternating copolymer of propylene and CO in the 0–550 K region

The temperature dependences of the heat capacity and the temperatures and enthalpies of physical transitions of the alternating copolymer of propylene and CO were studied in the 5–550 K region by adiabatic vacuum and dynamic calorimetry techniques. The heat of combustion of the copolymer was measured at 298.15 K in a calorimeter with a static bomb and an isothermal shield. The thermodynamic parameters of glass transition and fusing were estimated. The thermodynamic functions in the 0–450 K region and the thermodynamic characteristics of the formation of the copolymer from simple substances atT=298.15 K andp=101.325 kPa were calculated. The thermodynamic parameters of the alternating copolymerization of bulk propylene and CO were calculated in the 0–450 K region at standard pressure.     

On the Interpretation and Correlation of High‐Temperature Ignition Delays in Reactors with Varying Thermodynamic Conditions

Ignition delay time (IDT) is a useful global metric for fuel performance screening and a major target for kinetic modeling. Measurements of IDT are conceptually straightforward; however, interpretation could be complicated, especially for systems with changing temperature and pressure. Some experimental conditions in the high repetition rate miniature shock tube (HRRST) exhibit complex temperature and pressure state histories. To better interpret and correlate IDTs, especially those obtained in reactors with varying thermodynamic conditions, an inverse Livengood–Wu (L‐W) integral technique is applied to deconvolve the constant condition IDTs from measured IDTs in the HRRST using information on the varying state history. In this paper, the approximate problem is demonstrated using only the measured pressure history leading up to ignition, where the temperature history is estimated based on an isentropic assumption. The IDTs of several fuels were first measured in the HRRST including isooctane and acetone to represent those fuels without strong low‐temperature chemistry effects. Based on the measured pressure and approximated temperature history, measurements of IDTs in the HRRST compare very favorably with those measured using more conventional techniques, including conventionally sized shock tubes, via the inverse L‐W correlation with relaxed Newton iteration and genetic algorithm. This study demonstrates the feasibility of using a high throughput ignition testing facility, like the HRRST to extract the constant state IDT measured in regular shock tubes, assisted by the inverse L‐W correlation. It is expected with an independent temperature measurement available in the future, IDTs in a broader range of thermodynamic conditions and effects of heat loss could be better resolved.     

Modeling of Supramolecular Structure and Physicochemical Properties of the Propanone–Methanol Mixture

The results on modeling of the supramolecular organization and physicochemical properties of the propanone-methanol mixture are presented. An analysis of the excess thermodynamic functions (Gibbs energy, enthalpy, and entropy) and the permittivity of mixtures have been performed in the whole range of compositions and temperatures. It has been demonstrated that the model of supramolecular structure, taking into account the chain and cyclic association of methanol molecules and complexation of alcohol aggregates with propanone, describes the properties of the mixture. It established that both specific and universal interactions contribute to the positive deviations from the thermodynamic ideal solution behavior. Positive deviation of the dipole correlation factor from unity is due to a predominantly parallel orientation of the dipoles of the molecules in methanol aggregates and their complexes with propanone. The thermodynamic parameters of aggregation and structural parameters of aggregates have been determined. The cooperativity of H bonding was established. Distribution functions of the aggregate, according to size and structure, are presented. The manifestations of the supramolecular ordering on the physicochemical properties of the mixture are discussed.