scholarly journals Crystal Structure Optimization and Gibbs Free Energy Comparison of Five Sulfathiazole Polymorphs by the Embedded Fragment QM Method at the DFT Level

Crystals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 256 ◽  
Author(s):  
Xuan Hao ◽  
Jinfeng Liu ◽  
Hongyuan Luo ◽  
Yanqiang Han ◽  
Wenxin Hu ◽  
...  
Keyword(s):  
Free Energy ◽  
Gibbs Free Energy ◽  
Density Functional ◽  
Atomic Scale ◽  
Scale Model ◽  
Energy Calculation ◽  
Spectra Analysis ◽  
The Density Functional Theory ◽  
Antibiotic Drug ◽  
Experimental Crystal

Molecular crystal plays an important role in many fields of science and technology, but it often crystallizes in different polymorphs with different physical properties. To guide the experimental synthesis of candidate materials, the atomic-scale model is frequently used to predict the most stable polymorph and its structural properties. Here, we show how an ab initio method can be used to achieve a rapid and accurate prediction of sulfathiazole crystal polymorphs (an antibiotic drug), based on the Gibbs free energy calculation and Raman spectra analysis. At the atmospheric pressure and the temperature of 300 K, we demonstrate that form III (FIII) is the most stable structure of sulfathiazole. The agreement between the predicted and experimental crystal structures corresponds to the order of stability for five sulfathiazole polymorphs as FI < FV < FIV < FII < FIII, which is achieved by employing the density functional theory (DFT) calculations.

scholarly journals First-Principles Study of Mechanical and Thermodynamic Properties of Binary and Ternary CoX (X = W and Mo) Intermetallic Compounds

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1404
Author(s):  
Yunfei Yang ◽  
Changhao Wang ◽  
Junhao Sun ◽  
Shilei Li ◽  
Wei Liu ◽  
...  
Keyword(s):  
Free Energy ◽  
Thermodynamic Properties ◽  
Gibbs Free Energy ◽  
Density Functional ◽  
Vibrational Entropy ◽  
Functional Theory ◽  
Lattice Constants ◽  
The Density Functional Theory ◽  
Ductile Behavior ◽  
Pseudo Potential

In this study, the structural, elastic, and thermodynamic properties of DO19 and L12 structured Co3X (X = W, Mo or both W and Mo) and μ structured Co7X6 were investigated using the density functional theory implemented in the pseudo-potential plane wave. The obtained lattice constants were observed to be in good agreement with the available experimental data. With respect to the calculated mechanical properties and Poisson’s ratio, the DO19-Co3X, L12-Co3X, and μ-Co7X6 compounds were noted to be mechanically stable and possessed an optimal ductile behavior; however, L12-Co3X exhibited higher strength and brittleness than DO19-Co3X. Moreover, the quasi-harmonic Debye–Grüneisen approach was confirmed to be valid in describing the temperature-dependent thermodynamic properties of the Co3X and Co7X6 compounds, including heat capacity, vibrational entropy, and Gibbs free energy. Based on the calculated Gibbs free energy of DO19-Co3X and L12-Co7X6, the phase transformation temperatures for DO19-Co3X to L12-Co7X6 were determined and obtained values were noted to match well with the experiment results.

REEXAMINATION OF LOW ENERGY STRUCTURES OF ${\rm Au}_{4}^{-}$ AND Au4

2010 ◽  
Vol 09 (supp01) ◽  
pp. 1-7 ◽  
Author(s):  
YI GAO ◽  
YU ZHAO ◽  
X. C. ZENG
Keyword(s):  
Free Energy ◽  
Density Functional ◽  
Photoelectron Spectrum ◽  
Global Minimum ◽  
Low Energy ◽  
Basis Sets ◽  
Cluster Method ◽  
Energy Calculation ◽  
Couple Cluster ◽  
B3lyp Method

Low energy isomers of [Formula: see text] and Au4 were reexamined using the hybrid density functional B3LYP method and the couple-cluster method with the aug-cc-pVDZ-PP and aug-cc-pVTZ-PP basis sets. For [Formula: see text], the B3LYP method favors the zigzag isomer and the second order Moller–Plesset perturbation (MP2) total energy calculation favors the D2h rhombus isomer, whereas the couple-cluster singles and doubles with perturbative triples [CCSD(T)] level of theory favors the Y-shaped C2v isomer. The pyramid isomer is much higher in energy and could be easily excluded. The Gibbs free energy correction based on harmonic approximation suggests that the zigzag isomer is lower in free energy than the D2h rhombus isomer at 298.15 K. These results confirm that the Y-shaped C2v isomer is the global minimum at both 0 K and room temperature and is thus the major isomer to account for the experimental photoelectron spectrum. The zigzag isomer is suggested, as a minor isomer, to account for the weak second peak at 3.40 eV in the experimental photoelectron spectrum. For neutral Au4 , the zigzag isomer is more stable than D2h rhombus isomer at the B3LYP level and the D2h rhombus isomer is the global minimum on basis of all post Hartree–Fock levels of theory.

CHLORINE GAS SENSING OF SnO2 NANOCLUSTERS AS A FUNCTION OF TEMPERATURE: A DFT STUDY

2019 ◽  
Vol 26 (04) ◽  
pp. 1850172
Author(s):  
MUDAR AHMED ABDULSATTAR ◽  
ADEEBH L. RESNE ◽  
SHROK ABDULLAH ◽  
RIYADH J. MOHAMMED ◽  
NOON KADHUM ALARED ◽  
...  
Keyword(s):  
Free Energy ◽  
Gibbs Free Energy ◽  
Density Functional ◽  
Tin Dioxide ◽  
Energy Gap ◽  
Gas Sensing ◽  
Free Energy Calculations ◽  
Measured Temperature ◽  
Chlorine Molecule ◽  
Chlorine Gas

Density functional theory combined with Gibbs free energy calculations is used to study the sensing behavior of tin dioxide (SnO[Formula: see text] clusters towards chlorine gas molecules. Studied SnO2 clusters’ results show the known property of tin dioxide being an oxygen-deficient semiconductor with the preferred stoichiometry SnO[Formula: see text]. The kind of reactions that result in sensing Cl2 molecules is investigated. These include oxygen replacement, chlorine molecule dissociation and van der Waals attachment. Oxygen replacement shows an increase in energy gap which is the case experimentally. Optimum sensing operating temperature towards Cl2 molecules that results from the intersection of the highest SnO2 adsorption and desorption Gibbs free energy lines is at 275∘C in agreement with the experimentally measured temperature of 260∘C.

scholarly journals DFT Investigation of Hydrogen Atom Abstraction from NHC-Boranes by Methyl, Ethyl and Cyanomethyl Radicals—Composition and Correlation Analysis of Kinetic Barriers

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4509
Author(s):  
Hong-jie Qu ◽  
Lang Yuan ◽  
Cai-xin Jia ◽  
Hai-tao Yu ◽  
Hui Xu
Keyword(s):  
Free Energy ◽  
Hydrogen Atom ◽  
Gibbs Free Energy ◽  
Density Functional ◽  
Vibrational Energy ◽  
Hydrogen Atom Abstraction ◽  
Reaction Energy ◽  
Energy Barriers ◽  
Energy Correction ◽  
Kinetic Barriers

Understanding the hydrogen atom abstraction (HAA) reactions of N-heterocyclic carbene (NHC)-boranes is essential for extending the practical applications of boron chemistry. In this study, density functional theory (DFT) computations were performed for the HAA reactions of a series of NHC-boranes attacked by •CH2CN, Me• and Et• radicals. Using the computed data, we investigated the correlations of the activation and free energy barriers with their components, including the intrinsic barrier, the thermal contribution of the thermodynamic reaction energy to the kinetic barriers, the activation Gibbs free energy correction and the activation zero-point vibrational energy correction. Furthermore, to describe the dependence of the activation and free energy barriers on the thermodynamic reaction energy or reaction Gibbs free energy, we used a three-variable linear model, which was demonstrated to be more precise than the two-variable Evans–Polanyi linear free energy model and more succinct than the three-variable Marcus-theory-based nonlinear HAA model. The present work provides not only a more thorough understanding of the compositions of the barriers to the HAA reactions of NHC-boranes and the HAA reactivities of the substrates but also fresh insights into the suitability of various models for describing the relationships between the kinetic and thermodynamic physical quantities.

Development of a Suite of Computational Models for the Design of Ultralow-k SiCOH-based Materials

2012 ◽  
Vol 1428 ◽  
Author(s):  
Alexandra Cooper ◽  
Paulette Clancy
Keyword(s):  
Mechanical Properties ◽  
Density Functional ◽  
Computational Models ◽  
Experimental Studies ◽  
Atomic Scale ◽  
Scale Model ◽  
Simple Correlation ◽  
Functional Theory ◽  
Mechanical And Electrical Properties ◽  
Multiple Length Scales

ABSTRACTA computational model of amorphous SiCOH materials is described that will facilitate studies of SiCOH behavior under different thermal and mechanical stresses. This involved developing an atomic-scale model of an SiCOH thin film, which exhibited structural, mechanical and electrical properties in agreement with experimental studies. We developed a unique process for computationally creating the structure of SiCOH films. We created an algorithm for introducing and estimating porosity in the system, which provides detailed information about the system’s pore size distribution on multiple length scales. We used Density Functional Theory (DFT) to develop a simple correlation that calculates the dielectric constant of a large SiCOH structure based only on its atomic composition and volume. Finally, we confirmed the mechanical properties of the model using established Molecular Dynamics techniques. We verified that essential electronic and mechanical properties of the model structure reproduce experimental data for a representative SiCOH material within acceptable accuracy. We find the mechanical properties are significantly weakened by the presence of pendant carbon groups.

scholarly journals A density functional theory study of the oxygen reduction reaction on the (111) and (100) surfaces of cobalt(II) oxide

2019 ◽  
Vol 44 (2) ◽  
pp. 122-131
Author(s):  
Bangchang Qin ◽  
Yang Tian ◽  
Pengxiang Zhang ◽  
Zuoyin Yang ◽  
Guoxin Zhang ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Free Energy ◽  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Gibbs Free Energy ◽  
Density Functional ◽  
Rational Design ◽  
Reduction Reaction ◽  
Functional Theory ◽  
Associative Mechanism

Density functional theory calculations were employed to investigate the electrochemical oxygen reduction reaction on the (111) and (100) surfaces of cobalt(II) oxide. Different mechanisms were applied to evaluate the oxygen reduction reaction performance of cobalt(II) oxide structures in terms of the Gibbs free energy and density of states. A variety of intermediate structures based on associative and dissociative mechanisms were constructed and optimized. As a result, we estimated the catalytic activity by calculating the free energy of the intermediates and constructing free energy diagrams, which suggested that the oxygen reduction reaction Gibbs free energy on cobalt(II) oxide (111) and (100) surfaces based on the associative mechanism is smaller than that based on the dissociative mechanism, demonstrating that the associative mechanism should be more likely to be the oxygen reduction reaction pathway. Moreover, the theoretical oxygen reduction reaction activity on the cobalt(II) oxide (111) surface was found to be higher than that on the cobalt(II) oxide (100) surface. These results shed light on the rational design of high-performance cobalt(II) oxide oxygen reduction reaction catalysts.

Structural and elastic properties of ZrN and HfN: ab initio study

2014 ◽  
Vol 92 (9) ◽  
pp. 1058-1061 ◽  
Author(s):  
Anurag Srivastava ◽  
Bhoopendra Dhar Diwan
Keyword(s):  
Elastic Properties ◽  
Density Functional ◽  
Zirconium Nitride ◽  
Energy Calculation ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Hafnium Nitride ◽  
Zinc Blende ◽  
The Density Functional Theory ◽  
The Stability

The present paper discusses the density functional theory based stability analysis of zirconium nitride and hafnium nitride in its rocksalt (B1), CsCl (B2), and zinc blende (B3) type phases. The ground state total energy calculation approach of the system has been used through the generalized gradient approximation parameterized with revised Perdew–Burke–Ernzerhof as exchange correlation functional. The present theoretical analysis confirms the stability trend of phases from most stable to less stable as B1 → B2 → B3. The study also reports the analysis of elastic properties of these nitrides in its most stable B1-type phase.

scholarly journals Gibbs Free Energy Calculation of Mutation in PncA and RpsA Associated With Pyrazinamide Resistance

2020 ◽  
Vol 7 ◽  
Author(s):  
Muhammad Tahir Khan ◽  
Sajid Ali ◽  
Muhammad Tariq Zeb ◽  
Aman Chandra Kaushik ◽  
Shaukat Iqbal Malik ◽  
...  
Keyword(s):  
Free Energy ◽  
Gibbs Free Energy ◽  
Free Energy Calculation ◽  
Energy Calculation

scholarly journals Unified Assessment of the Effects of Van der Waals Interactions on the Structural and Electronic Properties of Some Layered Organic Solids κ-(BEDT-TTF)2X

Crystals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 348
Author(s):  
Predrag Lazić ◽  
Ognjen Milat ◽  
Branko Gumhalter ◽  
Silvia Tomić
Keyword(s):  
Density Functional ◽  
Van Der Waals ◽  
Detailed Examination ◽  
Test System ◽  
Van Der Waals Interactions ◽  
Electronic Band ◽  
Prototype Test ◽  
The Density Functional Theory ◽  
Structural And Electronic Properties ◽  
Experimental Crystal

Proper inclusion of van der Waals interactions (vdW) in ab initio calculations based on the density functional theory (DFT) is crucial to describe soft, organic, layered solids such as κ -(BEDT-TTF) 2 X . Since no consensus has been reached on the reliability of available vdW DFT functionals, most of the first principles calculations have been based on experimental crystal structure data without any structural optimization. Here, we explore optimal DFT-based schemes that account for the effects of vdW interactions on the structural and electronic band properties of three paradigmatic charge transfer salts, κ -(BEDT-TTF) 2 Cu 2 (CN) 3 , κ -(BEDT-TTF) 2 Ag 2 (CN) 3 , and κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl, for which a unified optimization of the structure is possible. Detailed examination of the prototype test system κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl shows that the optB88-vdW functional performs slightly better than the PBE-vdW and that the choice of pseudopotentials is critical to obtaining realistic results.

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