Structural and spectroscopic aspects of SCN(-)(H2O)n clusters and the temperature dependency of the isomers: a parallel tempering based approach
04 Mar 2019-Molecular Physics (Taylor & Francis)-Vol. 117, Iss: 5, pp 575-589
TL;DR: In this paper, parallel tempering has been used to explore the quantum chemical surface of SCN(−)(H2O)n system for n = 1−8 and the stretching frequencies and more specifically the shifts in O−H stretchi...
Abstract: In this work, parallel tempering has been used to explore the quantum chemical surface of SCN(−)(H2O)n system for n=1−8. The stretching frequencies and more specifically the shifts in –O–H stretchi...
01 Dec 1992
TL;DR: In this article, a stochastic optimisation procedure using simulated annealing for studying conformational changes in (MgF2)n clusters is presented, where the pathways for transformation between stable geometries through a...
Abstract: We present a stochastic optimisation procedure using simulated annealing for studying conformational changes in (MgF2)n clusters. The pathways for transformation between stable geometries through a...
TL;DR: In this article , the properties of organic aerosols containing amino acids or amides were investigated at the M06-2X/6-311++G(3df,3pd) level.
Abstract: Amino acids are important nitrogen-containing compounds and organic carbon components that exist widely in the atmosphere. The formation of atmospheric aerosols is affected by their interactions with amides. The dimers formed by glutamic acid (Glu) or protonated glutamic acid (Glu+) with three kinds of amide molecules (formamide FA, acetamide AA, urea U) and the hydrated clusters formed by Glu or Glu+, U molecules along with one to six water molecules were systematically studied at the M06-2X/6-311++G(3df,3pd) level. U is predicted to form a more stable structure with Glu/Glu+ than FA and AA by thermodynamics. If the concentration ratio of FA to U is less than 104, U will play a critical role in NPF. The degree of hydration in Glu+-mU-nW is higher than that of Glu-mU-nW (m = 0, 1; n = 0-6) clusters. Notably, Glu contributes more to the Rayleigh scattering properties than glutaric acid and sulfuric acid, and thus may lead to the destruction of atmospheric visibility. This study is helpful to better understand the properties of organic aerosols containing amino acids or amides.
TL;DR: To understand the working principles of the parallel tempering method, distribution of structures found in different replicas has been analyzed, and insights have been given as to how parallel Tempering can be use effectively to handle this problem effectively.
Abstract: The problem of studying structural transformation for going from one isomer to another through a transition state is one of considerable interest in chemistry. In this work, we would like to examine the efficiency of the replica exchange Monte Carlo strategy or parallel tempering to search potential energy surface describing the interaction between atoms in noble gas clusters. The systems chosen are both a pure noble gas cluster as well as those formed by two different noble gas entities. Location of minimal structures as well as transition state with the path connecting these three critical points has been carried out for different sizes. To understand the working principles of the parallel tempering method, distribution of structures found in different replicas has been analyzed and insights have been given as to how parallel tempering can be use effectively to handle this problem effectively.
TL;DR: In this paper, a method of "natural population analysis" was developed to calculate atomic charges and orbital populations of molecular wave functions in general atomic orbital basis sets, which seems to exhibit improved numerical stability and to better describe the electron distribution in compounds of high ionic character.
Abstract: A method of ‘‘natural population analysis’’ has been developed to calculate atomic charges and orbital populations of molecular wave functions in general atomic orbital basis sets. The natural analysis is an alternative to conventional Mulliken population analysis, and seems to exhibit improved numerical stability and to better describe the electron distribution in compounds of high ionic character, such as those containing metal atoms. We calculated ab initio SCF‐MO wave functions for compounds of type CH3X and LiX (X=F, OH, NH2, CH3, BH2, BeH, Li, H) in a variety of basis sets to illustrate the generality of the method, and to compare the natural populations with results of Mulliken analysis, density integration, and empirical measures of ionic character. Natural populations are found to give a satisfactory description of these molecules, providing a unified treatment of covalent and extreme ionic limits at modest computational cost.
TL;DR: A method for crystal structure prediction from ``scratch'' through particle-swarm optimization (PSO) algorithm within the evolutionary scheme and illustrates the promise of PSO as a major technique on crystal structure determination.
Abstract: We have developed a method for crystal structure prediction from ``scratch'' through particle-swarm optimization (PSO) algorithm within the evolutionary scheme. PSO technique is different with the genetic algorithm and has apparently avoided the use of evolution operators (e.g., crossover and mutation). The approach is based on an efficient global minimization of free-energy surfaces merging total-energy calculations via PSO technique and requires only chemical compositions for a given compound to predict stable or metastable structures at given external conditions (e.g., pressure). A particularly devised geometrical structure parameter which allows the elimination of similar structures during structure evolution was implemented to enhance the structure search efficiency. The application of designed variable unit-cell size technique has greatly reduced the computational cost. Moreover, the symmetry constraint imposed in the structure generation enables the realization of diverse structures, leads to significantly reduced search space and optimization variables, and thus fastens the global structure convergence. The PSO algorithm has been successfully applied to the prediction of many known systems (e.g., elemental, binary, and ternary compounds) with various chemical-bonding environments (e.g., metallic, ionic, and covalent bonding). The high success rate demonstrates the reliability of this methodology and illustrates the promise of PSO as a major technique on crystal structure determination.
TL;DR: A unified view of principles that underlie the stability of particles protected by thiolate or phosphine and halide ligands is provided and is best described by a “noble-gas superatom” analogy.
Abstract: Synthesis, characterization, and functionalization of self-assembled, ligand-stabilized gold nanoparticles are long-standing issues in the chemistry of nanomaterials. Factors driving the thermodynamic stability of well documented discrete sizes are largely unknown. Herein, we provide a unified view of principles that underlie the stability of particles protected by thiolate (SR) or phosphine and halide (PR3, X) ligands. The picture has emerged from analysis of large-scale density functional theory calculations of structurally characterized compounds, namely Au102(SR)44, Au39(PR3)14X6−, Au11(PR3)7X3, and Au13(PR3)10X23+, where X is either a halogen or a thiolate. Attributable to a compact, symmetric core and complete steric protection, each compound has a filled spherical electronic shell and a major energy gap to unoccupied states. Consequently, the exceptional stability is best described by a “noble-gas superatom” analogy. The explanatory power of this concept is shown by its application to many monomeric and oligomeric compounds of precisely known composition and structure, and its predictive power is indicated through suggestions offered for a series of anomalously stable cluster compositions which are still awaiting a precise structure determination.
TL;DR: In the past 30 years, Kohn-Sham density functional theory has emerged as the most popular electronic structure method in computational chemistry as mentioned in this paper, and it has been used to assess the ever-increasing number of approximate structures.
Abstract: In the past 30 years, Kohn–Sham density functional theory has emerged as the most popular electronic structure method in computational chemistry. To assess the ever-increasing number of approximate...
TL;DR: A selected set of the many applications that have become possible with the introduction of parallel tempering are mentioned, and several promising avenues for future research are suggested.
Abstract: We review the history of the parallel tempering simulation method. From its origins in data analysis, the parallel tempering method has become a standard workhorse of physicochemical simulations. We discuss the theory behind the method and its various generalizations. We mention a selected set of the many applications that have become possible with the introduction of parallel tempering, and we suggest several promising avenues for future research.