Theoretical Prediction of Gibbs Free Energies of Formation for Crystallineα-MOOH andα-M_2O_3 Based on a Linear Free-Energy Relationship

In the present study,the modified Sverjensky-Molling equation,derived from a linear-free energy relationship,is used to predict the Gibbs free energies of formation of crystalline phases ofα-MOOH （with a goethite structure）andα-M_2O_3（with a hematite structure）from the known thermodynamic properties of the corresponding aqueous trivalent cations（M^（3＋））.The modified equation is expressed asΔG_（f,M_VX）~0=a_（M_VX）ΔG_（0,M^（3＋））^（0）＋b_（M_VX）＋β_（M_VXγM^（3＋））,where the coefficients a_（M_VX）,b_（M_VX）,andβ_（M_VX） characterize a particular structural family of M_VX（M is a trivalent cation[M^（3＋）]and X represents the remainder of the composition of solid）;γ^（3＋）is the ionic radius of trivalent cations（M^（3＋））;ΔG_（f,M_VX）~0 is the standard Gibbs free energy of formation of M_vX;andΔG_（n,M^（3＋））~0 is the non-solvation energy of trivalent cations（M^（3＋））.By fitting the equation to the known experimental thermodynamic data,the coefficients for the goethite family（α-MOOH）are a_（M_VX）=0.8838,b_（M_VX）=-424.4431（kcal/mol）,andβ_（M_VX）=115（kcal/ mol.（？））,while the coefficients for the hematite family（α-M_2O_3）are a_（M_VX）=1.7468,b_（M_VX）=-814.9573（kcal/ mol）,andβ_（M_VX）=278（kcal/mol.（？））.The constrained relationship can be used to predict the standard Gibbs free energies of formation of crystalline phases and fictive phases（i.e.phases that are thermodynamically unstable and do not occur at standard conditions）within the isostructural families of goethite（α-MOOH）and hematite（α-M_2O_3）if the standard Gibbs free energies of formation of the trivalent cations are known.

Theoretical Prediction of the Photovoltaic Properties of BFBPD-PC61 BM System as a Promising Organic Solar Cell

In this work,the photovoltaic properties of BFBPD-PC61 BM system as a promising high-performance organic solar cell（OSC） were theoretically investigated by means of quantum chemistry and molecular dynamics calculations coupled with the incoherent charge-hopping model.Moreover,the hole carrier mobility of BFBPD thin-film was also estimated with the aid of an amorphous cell including 100 BFBPD molecules.Results revealed that the BFBPD-PC61 BM system possesses a middle-sized open-circuit voltage of 0.70 V,large short-circuit current density of 17.26 mA ·cm^-2,high fill factor of 0.846,and power conversion efficiency of 10%.With the Marcus model,in the BFBPD-PC61 BM interface,the exciton-dissociation rate,kdis,was predicted to be 2.684×10^13 s^-1,which is as 3-5 orders of magnitude large as the decay（radiative and non-radiative） one（10-8-10^10s^-1）,indicating a high exciton-dissociation efficiency of 100% in the BFBPD-PC61 BM interface.Furthermore,by the molecular dynamics simulation,the hole mobility of BFBPD thin-film was predicted to be as high as 1.265 × 10^-2 cm-2·V^-1·s^-1,which can be attributed to its dense packing in solid state.

Ab Initio Theoretical Prediction on Structures of Boron Cationic Cluster B_(17)^+

Four isomers of the three-dimensionally connected bare boron cationic cluster B were investigated by using ab initio molecular orbital theory at the HF/6-31G level. The results show that the D5h symmetric isomer of B is a possible isomer candidate of its stable geometries with closed structure.

Theoretical Prediction on Photovoltaic Properties of 4CI-BPPQ/ PC61BM System via Density Functional Theory Calculations

Designing and synthesizing high-performable electron donor materials are very important for fabricating organic solar cell devices with high power conversion efficiency （PCE）. In this work, quantum chemical and molecular dynamics calculations coupled with the Marcus-Hush charge transfer model were used to investigate the photovoltaic properties of 4Cl-BPPQ/PC61BM. Results reveal that 4Cl-BPPQ/PCrlBM system theoretically possesses a large open-circuit voltage （1.29 V）, high fill factor （0.90）, and over 9% PCE. Moreover, calculations also reveal that the 4Cl-BPPQ/PC61BM system has a middle-sized exciton binding energy （0.492 eV）, but relatively small charge-dissociation and charge-recombination reorganization energies （0.345 eV and 0.355 eV）. Based on the 4CI-BPPQ/PC61BM complex, the charge-dissociation rate constant, kdis, is estimated to be as large as 6.575× 10^12 s^-1, while the charge-recombination one, krec, is very small （〈 1.0 s^-1） under the same condition due to the very small driving force （AGree=-1.900 eV）. In addition, by means of an amorphous cell containing one hundred 4C1-BPPQ molecules, the hole carrier mobility of 4CI-BPPQ solid is estimated as high as 3.191 × 10^-3 cm^2·V^-1·s^-1. In brief, our calculation shows that 4Cl-BPPQ/PC61BM system is a very promising organic solar cell system, and is worth of making further device research by experiments.

Germanium-Carbdiyne: A 3D Well-Defined sp-Hybridized Carbon-Based Material with Superhigh Li Storage Property

Carbyne delivers various excellent properties for the existence of the larger number of sp-hybridized carbon atoms.Here,a 3D well-defined porous carbon material germanium-carbdiyne(Ge-CDY)which is comprised of only sp-hybridized carbon atoms bridging by Ge atoms has been developed and investigated.The unique diamond-like structure constructed by linear butadiyne bonds and sp 3-hybridized Ge atoms ensures the stability of Ge-CDY.The large percentage of conjugated alkyne bonds composed of sp-C guarantees the good conductivity and the low band gap,which were further confirmed experimentally and theoretically,endowing Ge-CDY with the potential in electrochemical applications.The well-defined 3D carbon skeleton of Ge-CDY provides abundant uniform nanopores,which is suitable for metal ions storage and diffusion.Further half-cell evaluation also demonstrated Ge-CDY exhibited an excellent performance in lithium storage.All those indicating sp-hybridized carbon-based materials can exhibit great potential to possess excellent properties and be applied in the field of energy,electronic,and so on.

Prediction of forming limit curve(FLC) for Al–Li alloy 2198-T3 sheet using diferent yield functions

The Forming Limit Curve （FLC） of the third generation aluminum-lithium （Al-Li） alloy 2198-T3 is measured by conducting a hemispherical dome test with specimens of different widths. The theoretical prediction of the FLC of 2198-T3 is based on the M-K theory utilizing respectively the von Mises, Hill＇48, Hosford and Barlat 89 yield functions, and the different predicted curves due to different yield functions are compared with the experimentally measured FLC of 2198-T3. The results show that though there are differences among the four predicted curves, yet they all agree well with the experimentally measured curve. In the area near the planar strain state, the predicted curves and experimentally measured curve are very close. The predicted curve based on the Hosford yield function is more accurate under the tension-compression strain states described in the left part of the FLC, while the accuracy is better for the predicted curve based on Hill＇48 yield function under the tension-tension strain states shown in the right part.

Strategic design and fabrication of MXenes-Ti_(3)CNCl_(2)@CoS_(2) core-shell nanostructure for high-efficiency hydrogen evolution

CoS_(2) is considered to be a promising electrocatalyst for hydrogen evolution reaction(HER).However,its further widespread applications are hampered by the unsatisfactory activity due to relatively high chemisorption energy for hydrogen atom.Herein,theoretical predictions of first-principles calculations reveal that the introduction of a Cl-terminated MXenes-Ti_(3)CNCl_(2) can significantly reduce the HER potential of CoS_(2)-based materials and the Ti_(3)CNCl_(2)@CoS_(2) core–shell nanostructure has Gibbs free energy of hydrogen adsorption(|ΔGH|)close to zero,much lower than that of the pristine CoS_(2) and Ti_(3)CNCl_(2).Inspired by the theoretical predictions,we have successfully fabricated a unique Ti_(3)CNCl_(2)@CoS_(2) core–shell nanostructure by ingeniously coupling CoS_(2) with a Cl-terminated MXenes-Ti_(3)CNCl_(2).Interface-charge transfer between CoS_(2) and Ti_(3)CNCl_(2) results in a higher degree of electronic localization and a formation of chemical bonding.Thus,the Ti_(3)CNCl_(2)@CoS_(2) core–shell nanostructure achieves a significant enhancement in HER activity compared to pristine CoS_(2) and Ti_(3)CNCl_(2).Theoretical calculations further confirm that the partial density of states of CoS_(2) after hybridization becomes more non-localized,and easier to interact with hydrogen ions,thus boosting HER performance.In this work,the success of oriented experimental fabrication of high-efficiency Ti_(3)CNCl_(2)@CoS_(2) electrocatalysts guided by theoretical predictions provides a powerful lead for the further strategic design and fabrication of efficient HER electrocatalysts.

Influence of modeling approaches and structural parameters on impact resistance of the human porous cranium

Failure mechanism and impact resistance of a human porous cranium are studied in detail by means of theoretical and numerical methods.It is hypothesized that pore distribution of a cranium directly affects cranial energy absorption,and a stretched beam model and a real beam model are taken as the example for the verification.Meanwhile,for the purpose of comparison with numerical results,a theoretical model is also proposed for the prediction of residual velocity and contact force of the impactor for an impacted skull.Compared with the real beam model,the stretched beam model containing through-thickness pores is easily deformed under the impact,thereby buffering well the external impact energy.The energy absorption efficiency of both the stretched beam model and real beam model is concerned with the threshold velocity for penetration which is directly related to the size of the structural damage area.Overall,there is good agreement between numerical and theoretical results.In addition,the effect of structural geometric parameters(shape and size of the impactor)on the impact resistance of the skull bone is theoretically investigated.The study provides reference for the evaluation of the energy absorption and failure mechanism of the skull under impact loads.