PCM Model Research Articles

Non-bonding interactions and non-covalent delocalization effects play a critical role in the relative stability of group 12 complexes arising from interaction of diethanoldithiocarbamate with the cations of transition metals Zn(II), Cd(II), and Hg(II): a theoretical study.

The chelating properties of diethanoldithiocarbamate (DEDC) and π-electron flow from the nitrogen atom to the sulfur atom via a plane-delocalized π-orbital system (quasi ring) was studied using a density functional theory method. The molecular structure of DEDC and its complexes with Zn(II), Cd(II), and Hg(II) were also considered. First, the geometries of this ligand and DEDC-Zn(II), DEDC-Cd(II), and DEDC-Hg(II) were optimized, and the formation energies of these complexes were then calculated based on the electronic energy, or sum of electronic energies, with the zero point energy of each species. Formation energies indicated the DEDC-Zn(II) complex as the most stable complex, and DEDC-Cd(II) as the least stable. Structural data showed that the N1-C2 π-bond was localized in the complexes rather than the ligand, and a delocalized π-bond over S7-C2-S8 was also present. The stability of DEDC-Zn(II), DEDC-Cd(II), and DEDC-Hg(II) complexes increased in the presence of the non-specific effects of the solvent (PCM model), and their relative stability did not change. There was π-electron flow or resonance along N1-C2-S7 and along S7-C2-S8 in the ligand. The π-electron flow or resonance along N1-C2-S7 was abolished when the metal interacted with sulfur atoms. Energy belonging to van der Waals interactions and non-covalent delocalization effects between the metal and sulfur atoms of the ligand was calculated for each complex. The results of nucleus-independent chemical shift (NICS) indicated a decreasing trend as Zn(II) < Cd(II) < Hg(II) for the aromaticity of the quasi-rings. Finally, by ignoring van der Waals interactions and non-covalent delocalization effects between the metal and sulfur atoms of the ligand, the relative stability of the complexes was changed as follows:[Formula: see text] Graphical Abstract Huge electronic cloud localized on Hg(II) in the Hg(II)-DEDC complex.

A density functional theory study on the interaction of dipicolinic acid with hydrated Fe2+ cation

The most feasible complexes formed between dipicolinic acid and hydrated Fe2+ cation (namely, [FeL(H2O)3] and [FeL2]) have been modeled using density functional theory. A comparison among several computational levels of theory and available X-ray data showed that the B3LYP/6-311G(d) computational level provides accurate geometrical parameters for geometry optimization of complexes. The energetics and thermochemistry of complexation reactions in the gas phase and solvated medium (PCM) were evaluated at the B3LYP/6-311G(d) and B3LYP/6-311++G(2df,pd)//B3LYP/6-311G(d) levels of theory. The calculated thermochemistry data exhibited high complexation energies for both complexes and decreasing in the exothermicity of complexation reactions when PCM model was included in the calculations. The calculated free energy changes of complexation reactions pointed to spontaneous procedures. Detailed analysis of energy levels and major composition of selected frontier orbitals were performed and the results suggested the higher stability for the [FeL(H2O)3] system than for [FeL2]. Based on QTAIM, several bond-indexes such as electron density at the bond critical points, the Laplacian of the electron density, ellipticity and the total energy density were utilized to analyze chemical bonding in these complexes. Natural bond orbital (NBO) analysis was carried out to provide more precise insight on the interactions and nature of the bonds established between the ligand and the metal ion.

Theoretical investigation of the addition reaction of the aluminum chlorosilylenoid H(2)SiAlCl(3) with ethylene.

The addition reaction of the aluminum chlorosilylenoid H2SiAlCl3 with ethylene was investigated using the M06-2X and QCISD methods for the first time. The calculated results demonstrate that the addition reaction proceeds via two pathways: path I involves just one transition state, while path II involves two transition states. Path I is more feasible dynamically, as it has a lower barrier height than path II. The effect of the solvent CH2Cl2 was taken into consideration using the PCM model. The results indicated that the addition reaction is less likely to occur in CH2Cl2 solvent than in vacuum. This work has therefore highlighted a new pathway for the synthesis of silicon heterocyclic compounds. Graphical Abstract Relative energies (in kJ·mol(-1)) of the stationary points along the potential energy surfaces of the addition reaction of H2SiAlCl3 with C2H4 (values in parentheses were calculated in CH2Cl2 solvent).

Theoretical prediction on the addition reaction of germylenoid H2GeFMgF with ethylene

The addition reaction of germylenoid H2GeFMgF with ethylene (C2H4) was first investigated in this work. All of the stationary points were optimized using the M062X method in conjunction with the 6-311[Formula: see text]G (d, p) basis set and the corresponding energies were calculated using the QCISD method with the 6-311[Formula: see text]G (d, p) basis set. The calculated results demonstrated that there are two different channels in the addition reaction of H2GeFMgF with C2H4, while only the channel I is feasible once the C2H4approaches H2GeFMgF in the proper conditions. The solvent effect upon the addition reaction was also investigated using PCM model. The results demonstrated that the tetrahydrofuran (THF) solvent could accelerate the addition reaction.

Incorporating Anthropogenic Influences into Fire Probability Models: Effects of Human Activity and Climate Change on Fire Activity in California.

The costly interactions between humans and wildfires throughout California demonstrate the need to understand the relationships between them, especially in the face of a changing climate and expanding human communities. Although a number of statistical and process-based wildfire models exist for California, there is enormous uncertainty about the location and number of future fires, with previously published estimates of increases ranging from nine to fifty-three percent by the end of the century. Our goal is to assess the role of climate and anthropogenic influences on the state’s fire regimes from 1975 to 2050. We develop an empirical model that integrates estimates of biophysical indicators relevant to plant communities and anthropogenic influences at each forecast time step. Historically, we find that anthropogenic influences account for up to fifty percent of explanatory power in the model. We also find that the total area burned is likely to increase, with burned area expected to increase by 2.2 and 5.0 percent by 2050 under climatic bookends (PCM and GFDL climate models, respectively). Our two climate models show considerable agreement, but due to potential shifts in rainfall patterns, substantial uncertainty remains for the semiarid inland deserts and coastal areas of the south. Given the strength of human-related variables in some regions, however, it is clear that comprehensive projections of future fire activity should include both anthropogenic and biophysical influences. Previous findings of substantially increased numbers of fires and burned area for California may be tied to omitted variable bias from the exclusion of human influences. The omission of anthropogenic variables in our model would overstate the importance of climatic ones by at least 24%. As such, the failure to include anthropogenic effects in many models likely overstates the response of wildfire to climatic change.

DFT estimates of water environment impact on the reversible 2e− + 2H+ oxidation of aniline tetramer

The PCM (IEFPCM) and CPCM implicit models of water environment have been embodied to the DFT calculations of the reversible 2e−+2H+ process of aniline tetramer. The molecular structure of six reactants as well as reaction energy characteristics of their six reactions have been determined and compared to the vacuum model.The clear difference in reaction energy between two types of processes, electron transfers and proton transfers, is the advantage of the solvent model approach in comparison to the most simple gas phase calculations. The results corresponding to the electron transfer reactions, namely the redox potentials, are much closer to empirical expectations than DFT determinations done for the vacuum environment of the isolated tetramer.

Theoretical study of the effect of ligand topology on Fe(IV)O and Ru(IV)O complex reactivities

Density functional theory calculations were carried out to clarify the effect of ligand topology on the stability and reactivity of cis-α-[FeIV(O)(BQCN)]2+ (Fe-2a), cis-β-[FeIV(O)(BQCN)]2+ (Fe-2b), cis-α-[RuIV(O)(BQCN)]2+ (Ru-2a) and cis-β-[RuIV(O)(BQCN)]2+ (Ru-2b) (BQCN=N,N′-dimethyl-N,N′-bis(8-quinolyl)-cyclohexanediamine). All the iron and ruthenium isomers possess the triplet ground states. The relative stability between the two iron isomers follows the order of Fe-2a>Fe-2b, which is in agreement with the conclusions of Hong et al. Moreover, the trend of the relative stability of the two ruthenium isomers is Ru-2a>Ru-2b. The Density-of-States spectrums represent that the contribution of BQCN ligand to 3Fe-2b is more than the corresponding contribution to 3Fe-2a. The iron isomers react with isopropylbenzene via a two-state reactivity pattern on competing triplet and quintet spin states, while the ruthenium isomers react with isopropylbenzene by a single-state mechanism, only on the triplet spin state. The H-abstraction is affected by the tunneling contribution, which can decrease the reaction barriers. By adding the ZPE correction, PCM model assessed by DFT-D3 (BJ) and the tunneling correction, the analysis of the trend of the hydrogen-abstraction reactions barriers shows that Fe-2a is the more reactive than Fe-2b with the higher FeIV/III redox potential. Moreover, for the ruthenium complexes, although Ru-2a is the more reactive than Ru-2b, only 0.6kcal/mol lower. Above all, the ligand topology has little effect on the reactivities of the [RuIV(O)(BQCN)]2+ complexes.

Tautomerization of pyrido[2′,1′:2,3]imidazo[4,5-B]quinoline-12-ylcyanide: A DFT study

The titled imidazo compound can exist as three tautomers: OH, CH, and NH forms. Firstly, the OH tautomer is produced, which can be tautomerized to the CH and NH tautomers via the intramolecularproton transfer. Herein, employing density functional theory and handling the solvent effects with the PCM model, the structural parameters, energy behavior, and also tautomerization mechanism of the tautomers are investigated. Based on the DFT results and the obtained-AIM parameters, the CH tautomer is considered to be the most stable one. Also, the CH tautomer is a kinetically and thermodynamically controlled product in tautomerization of the OH tautomer in a methanol solution.

0-0 Energies Using Hybrid Schemes: Benchmarks of TD-DFT, CIS(D), ADC(2), CC2, and BSE/GW formalisms for 80 Real-Life Compounds.

The 0–0 energies of 80 medium and large molecules have been computed with a large panel of theoretical formalisms. We have used an approach computationally tractable for large molecules, that is, the structural and vibrational parameters are obtained with TD-DFT, the solvent effects are accounted for with the PCM model, whereas the total and transition energies have been determined with TD-DFT and with five wave function approaches accounting for contributions from double excitations, namely, CIS(D), ADC(2), CC2, SCS-CC2, and SOS-CC2, as well as Green’s function based BSE/GW approach. Atomic basis sets including diffuse functions have been systematically applied, and several variations of the PCM have been evaluated. Using solvent corrections obtained with corrected linear-response approach, we found that three schemes, namely, ADC(2), CC2, and BSE/GW allow one to reach a mean absolute deviation smaller than 0.15 eV compared to the measurements, the two former yielding slightly better correlation with experiments than the latter. CIS(D), SCS-CC2, and SOS-CC2 provide significantly larger deviations, though the latter approach delivers highly consistent transition energies. In addition, we show that (i) ADC(2) and CC2 values are extremely close to each other but for systems absorbing at low energies; (ii) the linear-response PCM scheme tends to overestimate solvation effects; and that (iii) the average impact of nonequilibrium correction on 0–0 energies is negligible.

Structural and spectral properties of tartrato complexes of vanadium(V) from quantum chemical calculations

Structural and spectral properties of three complex anions of vanadium(V) with tartrato ligands were theoretically studied by all-electron DFT calculations employing various functionals, such as BP86, BLYP, B3LYP, BHHLYP, and the M06-family. Results were statistically evaluated, with the aim to find a reliable, fairly accurate, and yet computationally efficient combination of methods and basis sets to be used in computational chemistry of vanadium(V) complex anions at even larger scale. Subsequent vibrational analysis based upon BP86 and B3LYP data provided a fair agreement with the experimental vibrational spectra. Additionally, the absorption UV–Vis and the electronic circular dichroism spectra of studied compounds were simulated via time-dependent density functional theory calculations with the long-range corrected functionals (CAM-B3LYP, LC-ωPBE, and ωB97XD). Finally, the 51V NMR chemical shifts were calculated using the GIAO approach at the B3PW91 level. The solvent effect was simulated within the PCM model. Where available, the calculated spectral properties were compared with experimental data.

The solvatochromism of phenolate betaines: comparing different cavities of a polarized continuum model.

Two variations of the polarized continuum model employing default ("PCM model") and SMD radii ("SMD model") were compared for the reproduction of the solvatochromic behavior of Reichardt's betaine dye, and of eight other phenolate betaines that exhibit a negative, positive or an inverted solvatochromic behavior. Molecules were optimized at the CAM B3LYP/6-31+G(d,p) level of theory, and transition energies were calculated with the TD-DFT method. The PCM model failed to reproduce the negative and the inverted solvachromism of these dyes in protic solvents. The SMD model, though not entirely accounting for hydrogen-bond effects in small, polar hydroxylic solvents, should be recommended as a better alternative for the theoretical simulation of the solvatochromism of phenolate betaines in medium to highly polar solvents. Graphical Abstract A comparison of two polarized continuum models ("default PCM" and "PCM/SMD") for reproducing the solvatochromism of phenolate betaines, with nine examples of negative, positive, and inverted behavior.

A new exploration of the addition reaction of the silylenoid H2SiLiF with ethylene.

The addition reactions of the simplest silylenoid H2SiLiF with ethylene were studied theoretically. The geometries of the stationary points along the potential energy surfaces were optimized using DFT B3LYP method with the 6-311+G(d,p) basis set, and the single point energies were calculated at QCISD/6-311++G(d,p) level of theory. The theoretical calculations demonstrated that the addition reaction of H2SiLiF and C2H4 can occur through two different pathways. One is path A via a three-membered ring transition state, the other is path B, while through a four-membered ring transition state. The calculated energy barriers of path A and path B are 58.90 and 248.08 kJ∙mol(-1), respectively. Therefore, pathway A is more favorable than pathway B. The solvent effect on the addition reactions were investigated using the PCM model, and the calculated results indicated that in the THF solvent, the addition reaction is much easier than that in vacuum. The present work provided a new pathway to synthesize silicon heterocyclic compounds.

Study of noncovalent interactions of end-caped sulfur-doped carbon nanotubes using DFT, QTAIM, NBO and NCI calculations

In the current study, the interactions of carbon nanotube and sulfur-doped carbon nanotubes (SCNTs) with methanol, methanethiol, water and dihydrogen sulfide at on-body and dead-end positions of nanotubes have been studied. Interaction energies in the gas and solvent (via PCM model) were calculated using density functional theory calculations. Atomic charges, interaction energies, electron densities and their Laplacians at bond critical points have been calculated. Moreover, noncovalent interaction isosurfaces have been visualized using NCI index calculations. Interactions in gaseous phase were more favorable than those in solvent phase, and among considered solvents (benzene, chloroform and cyclohexane), cyclohexane showed the most preferred interactions. In addition, oxygen-bearing molecules (methanol and water) showed more favorable interactions compared with sulfur-bearing ones. NBO analyses revealed the stronger donor–acceptor interactions with methanol and methanethiol. QTAIM calculation results indicated the reasonable electron densities at BCPs, and the Laplacians of electron densities showed ionic-like (closed shell) interactions. Moreover, isosurfaces of these interactions were also studied to depict the interaction surfaces, and DOS plots for SCNTs were obtained to define their HOMO–LUMO levels and electric conduction properties. The increasing of the global softness and decreasing of total hardness was resulted by sulfur doping of nanotubes, which causes the heterodoped nanotubes to become less electrophilic species.

Correlations among experimental and theoretical NMR data to determine the absolute stereochemistry of darcyribeirine, a pentacyclic indole alkaloid isolated from Rauvolfia grandiflora

Darcyribeirine (1) is a pentacyclic indole alkaloid isolated from Rauvolfia grandiflora. Stereochemistry of 1 was previously proposed based on 1D (coupling constant data) and 2D (NOESY correlations) NMR techniques, having been established a configuration 3R, 15S, and 20R (isomer 1a). Stereoisomers of 1 (i.e., 1a–1h) can be grouped into four sets of enantiomers. Carbon chemical shifts and hydrogen coupling constants were calculated using BLYP/6-31G* theory level for the eight isomers of 1. Calculated NMR data of 1a–1h were correlated with the corresponding experimental data of 1. The best correlations between theoretical and experimental carbon chemical shift data were obtained for the set of enantiomers 1e/1f to structures in the gaseous phase and considering solvent effects (using PCM and explicit models). Similar results were obtained when the same procedure was performed to correlations between theoretical and experimental coupling constant data. Finally, optical rotation calculations indicate 1e as its absolute stereochemistry. Orbital population analysis indicates that the hydrogen bonding between N–H of 1e and DMSO is due to contributions of its frontier unoccupied molecular orbitals, mainly LUMO+1, LUMO+2, and LUMO+3.

Density Functional Theoretical Study on the Mechanism of Adsorption of 2-Chlorophenol from Water Using γ-Fe2O3 Nanoparticles

Using density functional theory, the mechanism of adsorption of 2-chlorophenol from water in the presence of γ-Fe2O3 nanoparticles was investigated. Fe2O3 nanoparticles were modelled using Fe6(OH)18(H2O)6 ring clusters. 2-chlorophenol can coordinate to the γ-Fe2O3 nanoparticles via its own OH or Cl groups. The process produces two intermediates which will be converted into final products through two pathways (Cl pathway and OH pathway). The activation energy and activation Gibbs free energy of the two pathways have been calculated and compared with each other. It was found that the OH pathway is under thermodynamic control and the C1 pathway is under kinetic control. All of the calculations were performed using a hybrid density functional method (B3LYP) in the solution phase (PCM model).

Are the reduction and oxidation properties of nitrocompounds dissolved in water different from those produced when adsorbed on a silica surface? A DFT M05-2X computational study.

The reduction and oxidation properties of four nitrocompounds (trinitrotoluene [TNT], 2,4-dinitrotoluene, 2,4-dinitroanisole, and 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one [NTO]) dissolved in water as compared with the same properties for compounds adsorbed on a silica surface were studied. To consider the influence of adsorption, cluster models were developed at the M05/tzvp level. A hydroxylated silica (001) surface was chosen to represent a key component of soil. The PCM(Pauling) and SMD solvation models were used to model water bulk influence. The following properties were analyzed: electron affinity, ionization potential, reduction Gibbs free energy, oxidation Gibbs free energy, and reduction and oxidation potentials. It was found that adsorption and solvation decrease gas phase electron affinity, ionization potential, and Gibbs free energy of reduction and oxidation, and thus, promote redox transformation of nitrocompounds. However, in case of solvation, the changes are more significant than for adsorption. This means that nitrocompounds dissolved in water are easier to transform by reduction or oxidation than adsorbed ones. Among the considered compounds, TNT was found to be the most reactive in an electron attachment process and the least reactive for an electron detachment transformation. During ionization, a deprotonation of adsorbed NTO was found to occur.

Comparative study of climate-change scenarios on groundwater recharge, southwestern Mississippi and southeastern Louisiana, USA

A geographic information system (GIS)-based water-budget framework has been developed to study the climate-change impact on regional groundwater recharge, and it was applied to the Southern Hills aquifer system of southwestern Mississippi and southeastern Louisiana, USA. The framework links historical climate variables and future emission scenarios of climate models to a hydrologic model, HELP3, to quantify spatiotemporal potential recharge variations from 1950 to 2099. The framework includes parallel programming to divide a large amount of HELP3 simulations among multiple cores of a supercomputer, to expedite computation. The results show that a wide range of projected potential recharge for the Southern Hills aquifer system resulted from the divergent projections of precipitation, temperature and solar radiation using three scenarios (B1, A2 and A1FI) of the National Center for Atmospheric Research’s Parallel Climate Model 1 (PCM) and the National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Lab’s (GFDL) model. The PCM model projects recharge change ranging from −33.7 to +19.1 % for the 21st century. The GFDL model projects less recharge than the PCM, with recharge change ranging from −58.1 to +7.1 %. Potential recharge is likely to increase in 2010–2039, but likely to decrease in 2070–2099. Projected recharge is more sensitive to the changes in the projected precipitation than the projected solar radiation and temperature. Uncertainty analysis confirms that the uncertainty in projected precipitation yields more changes in the potential recharge than in the projected temperature for the study area.

Structure ofH2GeFMgFand its insertion reactions withRH(R=F,OH,NH2)

The structures of the germylenoid H2GeFMgF and its insertion reactions with RH ( R = F , OH , NH2) were studied using the DFT B3LYP and QCISD approaches for the first time. The geometries of all of the stationary points were optimized at the B3LYP/6-311+G (d, p) level of theory. And then the QCISD/6-311++G (d, p) single-point energies were calculated. The solvent effects on the geometries and insertion reactions were also computed using the PCM model. The calculated results suggested that H2GeFMgF had three equilibrium configurations, in which the p-complex structure had the lowest energy and was the most stable structure. The isomerization reactions among the three complexes had been studied. For the insertion reactions of H2GeFMgF with RH ( R = F , OH , NH2), along the potential energy surface, there were one transition state and one intermediate which connected the reactants and the products. For the three insertion reactions the mechanisms are identical. However, under the same conditions the insertion reactions should occur easily in the order of H - F &gt; H - OH &gt; H - NH2. The solvent effect calculations suggested the larger the solvent polarity is, the easier the reaction will be.

Computational Study of the Stability of Tautomers and equilibrium constants of Cyanuric acid (CA) in Different solvents.

In the present investigation, the tautomeric and equilibrium of Cyanuric acid has been studied using Hartifock (HF) method in the gas phase and different solvents using the PCM model. The relative energies of these tautomers have been calculated at the HF level of theory using 6-311++ G (d,p) basis set. Energetics and relative stabilities of the tautomers were compared and analyzed in both the gaseous and different solvents. The results indicate that the keto tautomer (CA1) is the most stable form in the gas phase and other solvents. The order of stability of isomers was found to be CA1 &gt; CA3&gt; CA11&gt; CA2&gt; CA6&gt; CA10&gt; CA7&gt; CA4&gt; CA5&gt; CA9&gt;CA8. Having the largest dipole moment the CA8 tautomer is expected to have the strongest interaction with polar solvents. The HF method calculated tautomeric equilibrium constants with respect to the most stable tautomer CA1 of Cyanuric acid both in the gas and in different solvents. The of the equilibrium constants calculated starting from the general outline of interconversion.

Density Functional Theory Calculations on Ni—Ligand Bond Dissociation Enthalpies

The formation and breaking of Ni—L (L=N-heterocyclic carbene, tertiary phosphine etc.) bond is involved in many Ni-catalyzed/mediated reactions. The accurate prediction of Ni—L bond dissociation enthalpies (BDEs) is potentially important to understand these Ni-complex involving reactions. We assess the accuracy of different DFT functionals (such as B3LYP, M06, MPWB1K, etc.) and different basis sets, including both effective core potentials for Ni and the all electron basis sets for all other atoms in predicting the Ni-L BDE values reported recently by Nolan et al. [J. Am. Chem. Soc. 125, 10490 (2003) and Organometallics 27, 3181 (2008)]. It is found that the MPWB1K/LanL2DZ:6-31+G(d,p)//MPWB1K/LanL2DZ:6-31G(d) method gives the best correlations with the experimental results. Meanwhile, the solvent effect calculations (with CPCM, PCM, and SMD models) indicate that both CPCM and PCM perform well.