Fluorination on cyclopentadithiophene-based hole-transport materials for high-performance perovskite solar cells.

A new class of fluorinated cyclopenta[2,1-b:3,4-b']dithiophene (CPDT)-based small molecules, namely YC-oF, YC-mF, and YC-H, are demonstrated as hole-transporting materials (HTMs) for high-performance perovskite solar cells (PSCs). PSCs employing YC-oF as the HTM delivered an excellent efficiency of 22.41% with encouraging long-term stability.

Detection of nitrofurazone with metal-organic frameworks and reduced graphene oxide composites: insights from molecular dynamics simulations.

Two-dimensional metal-organic framework (MOF) composites were produced by incorporating Fe-MOFs into reduced graphene oxide (rGO) nanosheets to form Fe-MOF/rGO composites by hydrothermal synthesis. SEM, TEM, XRD, XPS, and measurements of contact angles were used to characterize the composites. TEM studies revealed that the rod-like-shaped Fe-MOFs were extensively dispersed on the rGO sheets. Incorporating Fe-MOF into rGO significantly improves performance due to the large surface area, chemical stability, and high electrical conductivity. The response signals for the electrochemical sensing performance of Fe-MOF/rGO-modified electrodes to nitrofurazone (NFZ) were significantly enhanced. Differential pulse voltammetry was used to detect the NFZ, and the MOF/rGO sensor possesses a lower detection limit (0.77µM) with two dynamic ranges from 0.6-60 to 128-499.3 µM and high sensitivity (1.909 µA·mM-1·cm-2). Moreover, the anti-interference properties of the sensor were quite reproducible and stable. To understand the mechanism responsible for the enhanced sensing performance of the composite, grand canonical Monte Carlo calculations were performed for Fe-MOF/rGO composites with five unit cells of Fe-MOF and four layers of rGO. We attributed the improvement to the fact that the interface between the Fe-MOF and rGO absorbed increased NFZ molecules. The findings reported herein confirm that such Fe-MOF/rGO composites have significantly improved electrochemical performance and practical applicability of sensing nitrofurazone.

Electrochemical characterization of and theoretical insight into a series of 2D MOFs, [M(bipy)(C4O4)(H2O)2]·3H2O (M = Mn (1), Fe (2), Co (3) and Zn (4)), for chemical sensing applications.

The electrochemical sensing applications of a series of water-stable 2D metal-organic framework (MOF)-modified screen-printed carbon electrodes (SPCEs) are reported. The MOF materials in this study are [M(bipy)(C4O4)(H2O)2]·3H2O, in which bipy = 4,4'-bipyridine and M = Mn, Fe, Co and Zn. The MOF materials are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), showing that the MOFs have a layer-by-layer rod structure with a smooth surface. We use the nitrofurazone molecule as a probe to investigate the influence of the metal ions of MOFs on electrochemical sensing ability. Cyclic voltammetry demonstrated that the Mn-MOF electrode of interest delivered stronger signals than that of other electrodes. Through first-principles calculations, we also revealed that the change in the spin polarization of divalent metal ions passing from the free ion state to the MOF environment appeared to be significantly correlated with the enhancement in the peak response current. The theoretical and experimental results consistently indicate that Mn-MOF has the smallest bandgap and good sensitivity among these MOF materials. Accordingly, we proposed a simple model to illustrate this observation and disclosed the importance of the electron configuration of the transition metal constructing the MOF materials used in improving electrochemical sensing applications.

Discrete Solvent Reaction Field Calculations for One- and Two-Photon Absorptions of Solution-Phase Dimethylaminonitrostilbene Molecule.

Based on the configurations generated by molecular dynamics (MD) simulations using the on-the-fly density-functional tight-bonding (DFTB) force field, we investigated performance of the discrete solvent reaction field (DRF) model coupled to time-dependent density functional theory (TD-DFT) for solvatochromic effect of one- and two-photon absorption phenomena. Dimethylaminonitrostilbene (DANS) molecule solvated in chloroform, dichloromethane, and dimethyl sulfoxide solvents was selected as a model system for our research purpose. For every selected MD/DFTB configuration, within the context of the DRF, solute molecule is represented by TD-DFT and solvent molecules are described by atomic charges and polarizabilities. The calculated one-photon absorption energies reproduce well the positive solvatochromic behavior of solvated DANS and are in good agreement with available experimental data. For the two-photon absorption cross section, even though our approach overshot the experimental data by about 20% in absolute magnitude, experimentally observed solvatochromic change was captured qualitatively in this work. At last, we examined the contributions of atomic charges and polarizabilities of solvent molecules to the solvatochromic shifts of properties of interest.

Calculations of Electronic Excitation Energies and Excess Electric Dipole Moments of Solvated p-Nitroaniline with the EOM-CCSD-PCM Method.

We present computational evidence utilizing vertical electronic excitation energies and the corresponding excess dipole moments of solvated p-nitroaniline ( pNA). The properties of interest are calculated by employing the equation of motion coupled cluster together with single and double excitations (EOM-CCSD). Solvent effects are included through the polarizable continuum model (PCM) with the state-specific (SS) formalism and the perturbation theory energy and density (PTED) approach. We examine the ground state equilibrium geometry of pNA in different environments to yield the symmetry of the stable conformer of solvated pNA is C s but is also C2 v. By employing the calculated vertical excitation energies overestimate experiment, our calculations confirm the consistency of the calculated excess dipole moments with comparable documented results. Lastly, specific to this study, dissimilar environmental models, such as the linear response (LR), and variants of the corrected linear response (cLR and cLR0) formalisms in the context of the EOM-CCSD-PCM-PTED, are assessed against those from the SS formalism.

Density functional theory calculations of dynamic first hyperpolarizabilities for organic molecules in organic solvent: comparison to experiment.

Against experimental values obtained from solution-phase dc electric field induced second-harmonic generation measurements at a fundamental wavelength of 1910 nm, the performance of 20 exchange-correlation functionals in density functional theory in evaluation of solvent modulated dynamic first hyperpolarizabilities of 82 organic molecules in chloroform, 1,4-dioxane, and/or dichloromethane was evaluated. The used exchange-correlation functionals consisted of generalized gradient approximation (GGA), meta-GGA, global hybrids, and range-separated hybrids. The PCM-X/6-311+G(2d,p)//PCM-B3LYP/6-31G(2df,p) level of theory was employed. The calculated results showed functionals with the exact asymptote of the exchange potential gave satisfying linear correlation with R(2) of 0.95 between experimental data and theoretical values. With a linear correction, these functionals also provided a better accuracy with mean absolute error of 5 × 10(-30) esu than other functionals. The solvent effect and solvation scheme on the calculated property were also studied.

Computational study of static first hyperpolarizability of donor-acceptor substituted (E)-benzaldehyde phenylhydrazone.

Various hybrid functionals (B3LYP, B97-2, PBE0, BMK, BH&HLYP, CAM-B3LYP, and LC-ωPBE) implemented in density functional theory were applied to give estimate of static first hyperpolarizabilty (ß(0)) of (E)-benzaldehyde phenylhydrazone designated as (E)-BPH. Against those of MP2 computations as a function of the underlying density functional, good agreement was obtained with the BH&HLYP and CAM-B3LYP functionals. The LC-ωPBE functional and the B3LYP, PBE0, B97-2, and BMK functionals underestimated and overestimated ß(0), respectively. The basis set effect on the calculated ß(0) was also investigated. It turned out that the 6-311+G(2d,p) basis set provided excellent converged value of ß(0). On the basis of the calculated results, we investigated the substituent effect on ß(0) of donor-acceptor (D-A) substituted (E)-BPH systematically by using the BH&HLYP and CAM-B3LYP computations with the 6-311+G(2d,p) basis set. We proposed a Zwitterion structure to explain the calculated trend in the substituent effect and the enhanced hyperpolarizability of type II compounds (A-(E)-BPH-D) than type I compounds (D-(E)-BPH-A). Natural bonding orbital analysis carried out at BH&HLYP/6-311+G(2d,p)//B3LYP/6-31G(2df,p) level of theory substantiated the claim.

Gibbs energy of activation for thermal isomerization of (1Z)-acetaldehyde hydrazone and (1Z)-acetaldehyde N,N-dimethylhydrazone by Gaussian-4 theory and CCSD(T)/CBS computations.

In this article, we examined the Gibbs energy of activation for the Z/E thermal isomerization reaction of (1Z)-acetaldehyde hydrazone and (1Z)-acetaldehyde N,N-dimethylhydrazone, at 298.15 K in the solvent of cyclohexane. We carried out computations employing both the Gaussian-4 (G4) theory and the coupled cluster method using both single and double substitutions and triple excitations noniteratively, CCSD(T). The CCSD(T) energy is extrapolated to the complete basis set (CBS). We compared the calculated results to the available experimental observation. It appeared that both G4 and CCSD(T)/CBS computations overestimated the experimental value by as much as about 6 and 12 kcal/mol in the present two cases. We discussed possible sources of error and proposed the experimental kinetic data could be questionable.

A diffusion quantum Monte Carlo study on the lowest singlet and triplet electronic states of BN molecule.

Ab initio calculation of both the lowest singlet and triplet electronic states of BN has been performed by the fixed-node Ornstein-Uhlenbeck diffusion quantum Monte Carlo method with the floating spherical Gaussian orbitals and spherical Gaussian geminals. The Monte Carlo calculation gives equilibrium bond lengths and equilibrium harmonic frequencies of 1.3317(7) A and 1529(7) cm(-1), respectively, for the lowest triplet state and 1.2751(7) A and 1709(8) cm(-1), respectively, for the lowest singlet state. Also, the Monte Carlo calculation reports an energy separation of 178(83) cm(-1) between the two electronic states and recommends the ground state is the lowest triplet state.

Accuracy of a random-walk-based approach in the determination of equilibrium bond lengths and harmonic frequencies for some doublet first-row diatomic radicals.

The accuracy of equilibrium bond lengths and harmonic frequencies for 12 doublet first-row diatomic radicals is presented as predicted by the fixed-node diffusion quantum Monte Carlo method based on the Ornstein-Uhlenbeck random walk guided by the floating spherical Gaussian orbital and spherical Gaussian geminal-type trial wave function. Compared to the experimental determined values, the random-walk-based approach gives the absolute mean deviations of 0.0019 A and 18 cm-1 for the equilibrium bond length and harmonic frequency, respectively. We also compare the random-walk-based results with some coupled-cluster-based values.

Theoretical study of transition state structure and reaction enthalpy of the F + H2-->HF + H reaction by a diffusion quantum Monte Carlo approach.

Ab initio calculations of transition state structure and reaction enthalpy of the F + H2-->HF + H reaction has been carried out by the fixed-node diffusion quantum Monte Carlo method in this study. The Monte Carlo sampling is based on the Ornstein-Uhlenbeck random walks guided by a trial wave function constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals. The Monte Carlo calculated barrier height of 1.09(16) kcal/mol is consistent with the experimental values, 0.86(10)/1.18(10) kcal/mol, and the calculated value from the multireference-type coupled-cluster (MRCC) calculation with the aug-cc-pVQZ(F)/cc-pVQZ(H) basis set, 1.11 kcal/mol. The Monte Carlo-based calculation also gives a similar value of the reaction enthalpy, -32.00(4) kcal/mol, compared with the experimental value, -32.06(17) kcal/mol, and the calculated value from a MRCC/aug-cc-pVQZ(F)/cc-pVQZ(H) calculation, -31.94 kcal/mol. This study clearly indicates a further application of the random-walk-based approach in the field of quantum chemical calculation.

The accuracy of diffusion quantum Monte Carlo simulations in the determination of molecular equilibrium structures.

For a test set of 17 first-row small molecules, the equilibrium structures are calculated with Ornstein-Uhlenbeck diffusion quantum Monte Carlo simulations guiding by trial wave functions constructed from floating spherical Gaussian orbitals and spherical Gaussian geminals. To measure performance of the Monte Carlo calculations, the mean deviation, the mean absolute deviation, the maximum absolute deviation, and the standard deviation of Monte Carlo calculated equilibrium structures with respect to empirical equilibrium structures are given. This approach is found to yield results having a uniformly high quality, being consistent with empirical equilibrium structures and surpassing calculated values from the coupled cluster model with single, double, and noniterative triple excitations [CCSD(T)] with the basis sets of cc-pCVQZ and cc-pVQZ. The nonrelativistic equilibrium atomization energies are also presented to assess performance of the calculated methods. The mean absolute deviations regarding experimental atomization energy are 0.16 and 0.21 kcal/mol for the Monte Carlo and CCSD(T)/cc-pCV(56)Z calculations, respectively.

Electron affinities with diffusion quantum Monte Carlo for C2 and BO molecules.

To verify the performance of the fixed-node diffusion quantum Monte Carlo method in electron affinities calculations, the adiabatic electron affinities of C(2) and BO molecules calculated by the fixed-node Ornstein-Uhlenbeck diffusion quantum Monte Carlo simulations guiding by trial wave functions constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals are presented in this work. The random walk based results, 3.264(43) and 2.507(32) eV for C(2) and BO, respectively, are compared with the available best experimental determined values, 3.269(6) and 2.508(8) eV for C(2) and BO, respectively, and the results of other theoretical calculations.

A diffusion quantum Monte Carlo study of geometries and harmonic frequencies of molecules.

This article describes an approach in determination of equilibrium geometries and harmonic frequencies of molecules by the Ornstein-Uhlenbeck diffusion quantum Monte Carlo method based on the floating spherical Gaussians. In conjunction with a projected and renormalized Hellmann-Feynman gradient and an electronic energy at variational Monte Carlo and diffusion quantum Monte Carlo, respectively, the quasi-Newton algorithm implemented with the Broyden-Fletcher-Goldfarb-Shanno updated Hessian was used to find the optimized molecular geometry. We applied this approach to N2 and H2O molecules. The geometry and harmonic frequencies calculated were consistent with some sophisticated ab initio calculated values within reasonable statistical uncertainty.

Diffusion quantum Monte Carlo for equilibrium structures and harmonic frequencies of ethane and ozone molecules.

Application of the Ornstein-Uhlenbeck diffusion quantum Monte Carlo method in combination with a trial wave function constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals to studies on the equilibrium structures and harmonic frequencies of ethane and ozone is presented. These Monte Carlo computed results are compared with those of experiments as well as the coupled cluster methods with the correlation consistent basis sets for the two molecules. For ozone, we also compare the Monte Carlo results with the results from multireference calculations.

Ornstein-Uhlenbeck diffusion quantum Monte Carlo study on the bond lengths and harmonic frequencies of some first-row diatomic molecules.

This article accesses the performance of the Ornstein-Uhlenbeck diffusion quantum Monte Carlo with regard to the calculation of molecular geometries and harmonic frequencies of H2, LiH, HF, Li2, LiF, CO, N2, and F2 molecules. A comparison of the results for the eight first-row diatomic molecules from experiments, CCSD(T)/6-311G(3df,3pd) and CCSD(T)/cc-pV5Z levels of theory as well as our work is given. The results presented show that quantum Monte Carlo is becoming powerful tools for ab initio electronic structure calculations.