Corrected Density Functional Theory Research Articles

Individual Identification of DNA Nucleobases on Atomically Thin Black Phosphorene Nanoribbons: van der Waals Corrected Density Functional Theory Calculations

Monolayer-based nanodevices hold great promise for the next-generation sequencing (biomolecular sensing/DNA sequencing)-based applications. In this study, we have investigated the interaction of the four nucleobases (adenine, guanine, thymine, and cytosine) on a phosphorene nanoribbon-based device armchair phosphorene nanoribbon (APNR) for individual identification of DNA nucleobases. Using the van der Waals corrected (PBE + vdW) density functional theory calculations, we have computed and analyzed the effect of interaction on the transmission properties of the APNR-based nanodevice. The change in the electronic transport properties of APNR when nucleobases are physisorbed has been investigated by using the nonequilibrium Green’s function calculations. The coupling strength is different to some extent for different nucleobases, resulting in different transmission dips due to Fano resonance.

Modelling the adsorption of natural organic matter on Ag (111) surface: Insights from dispersion corrected density functional theory calculations

Understanding the nature of the interactions between natural organic matter (NOM) and engineered nanoparticles (ENPs) is of crucial importance in understanding the fate and behaviour of engineered nanoparticles in the environment. In the present study, dispersion-corrected density functional theory (DFT-D) has been used to elucidate the molecule-surface interactions of higher molecular weight (HMW) NOM ambiguously present in the aquatic systems, namely: humic acid (HA), fulvic acid (FA) and protein Cryptochrome (Cry) on Ag (111) surface. Investigations were done in the gas phase and to mimic real biological environment, water has been used as a solvent within the conductor-like screening model (COSMO) framework. The calculated adsorption energies for HA, FA and Cry on Ag (111) surface were −27.90 (−18.45) kcal/mol, −38.28 (−18.68) kcal/mol and −143.89 (−150.82) kcal/mol respectively in the gas (solvent) phase and the equilibrium distances between the surface and HA, FA and Cry molecules were 1.87 (2.18) Å, 2.31(2.31) Å and 1.91 (1.70) Å respectively in the gas (solvent) phase. In both gas and water phase Cry showed stronger adsorption which means it has a stronger interaction with Ag (111) surface compared to HA and FA. The results for adsorption energy, solvation energy, isosurface of charge deformation difference, total density of state and partial density of states indicated that indeed these chosen adsorbates do interact with the surface and are favourable on Ag (111) surface. In terms of charge transfer, one of many calculated descriptors in this study, electrophilicity (ω) concur that charge transfer will take place from the adsorbates to Ag (111) surface.

Two-dimensional metal carbide comrade for tracing CO and CO2

Present work aims to develop a two-dimensional graphene-like honeycomb AlC nanostructure as a potential gas sensor to efficiently capture the CO and CO2 gas molecules for purification of pollutants exhausted from fuel engines. Structural, dynamical, electronic and sensing properties of newly predicted hexagonal AlC monolayer (h-AlC) are investigated through first principles calculations based on density functional theory (DFT). Our studies report metallic nature of h-AlC. The real frequency of phonon modes in phonon dispersion curves (PDC) indicates dynamical stability of the h-AlC structure. The sensing ability of the h-AlC increases through the substitution of nearby radii elements B, N, P, and Si without any structural distortion in h-AlC. All calculations of adsorption energy, electronic density of states (DOS), charge transfer mechanism and work function analysis are performed with dispersion corrected density functional theory. The P substituted AlC (P-AlC) shows a strong binding with CO and CO2 molecules with an adsorption energy of −1.069 eV and −0.848 eV respectively. The work function calculation and shorter recovery time (in Peco sec.) of the monolayer confirm its novelty as a sensor.

Sensitivity enhancement of stanene towards toxic SO2 and H2S

Adsorption of S-containing gases on pristine, defective, and heteroatom doped stanene is studied for gas sensing applications by van der Waals corrected density functional theory. SO2 and H2S gas molecules are found to bind to pristine stanene too weakly to alter the electronic properties sufficiently for efficient gas sensing (binding energy of −0.20 and −0.33 eV, respectively). We demonstrate that vacancies and heteroatom doping can enhance the binding energy to −1.67 and −0.74 eV, respectively. It is found that presence of mono-vacancies, tri-vacancies, and In dopants at low concentrations in stanene results in considerable variations of the electronic properties in contact with S-containing gases, thus transforming stanene into an efficient sensing material.

Electronic Structure of a Semiconducting Imine-Covalent Organic Framework.

Imine COF (covalent organic framework) based on the Schiff base reaction between p-phenylenediamine (PDA) and benzene-1,3,5-tricarboxaldehyde (TCA) was prepared on the HOPG-air (air=humid N2 ) interface and characterized using different probe microscopies. The role of the molar ratio of TCA and PDA has been explored, and smooth domains of imine COF up to a few μm are formed for a high TCA ratio (>2) compared to PDA. It is also observed that the microscopic roughness of imine COF is strongly influenced by the presence of water (in the reaction chamber) during the Schiff base reaction. The electronic property of imine COF obtained by tunneling spectroscopy and dispersion corrected density functional theory (DFT) calculation are comparable and show semiconducting nature with a band gap of ≈1.8 eV. Further, we show that the frontier orbitals are delocalized entirely over the framework of imine COF. The calculated cohesive energy shows that the stability of imine COF is comparable to that of graphene.

DFT+U in Dudarev's formulation with corrected interactions between the electrons with opposite spins: The form of Hamiltonian, calculation of forces, and bandgap adjustments.

Hubbard corrected density functional theory (DFT) methods, such as the DFT+U approach in Dudarev's approximation, are widely used for the description of energetics and electronic structure of strongly correlated materials, providing higher level of accuracy than local DFT calculations (e.g., local density approximation or generalized gradient approximation). However, the DFT+U method in Dudarev's formulation limits the introduced corrections to interactions between the electrons within the same spin channel, whereas interactions between the electrons with opposite spins are still treated using local DFT functional (e.g., Perdew-Burke-Ernzerhof). In recent years, the need for correction of these interactions between the electrons with opposite spins has been recognized and additional terms have been added to the Hubbard term to reflect it. Although such extended DFT+U functionals have been proposed, the form of respective Hamiltonian operator, defined as a total energy derivative over density with appropriate treatment of double counting corrections due to additional Hubbard terms, has not been explicitly presented. In this work, we provide an expression for such a type of Hamiltonian, which contains the respective double counting correction contributions. This formulation also allows evaluation of atomic forces, using computational settings discussed herein. In addition, we also introduce adjustments for too narrow theoretical bandgaps, using scissor operator technique. This allows for a greater level of corrections of energetics and magnetic properties of studied transition metal compounds, avoiding possible unphysical overlap between occupied and unoccupied electronic bands.

Carbon-Based Anode Materials for Alkali Metal Ion Batteries – Atomic Scale Studies of Defects, Functional Groups, and Electrolytes and Their Impact on Metal Storage and Diffusion

Sodium ion batteries (SIBs) and potassium ion batteries (PIBs) are currently being investigated as credible post lithium ion batteries (LIBs) technologies.1–3 Due to their low cost, natural abundance, suitability for LIBs, SIBs, and PIBs, carbon-based anode materials, especially hard carbons, have gained scientific interest.3–6 These materials need to be optimized for high performance batteries. However, the molecular structure of hard carbons is complex, and the atomistic understanding of metal ion storage and intercalation/de-intercalation during charge and discharge is limited. Hence, we in this work aim to shed light on these mechanisms through systematic computational modelling of LIB, SIB, and PIB carbon-based anode materials. Experimental studies have postulated that surface defects, and functional groups (especially oxygen-containing such), can have a marked effect on metal storage.4,7–1 1 To investigate this, we have used dispersion corrected density functional theory (DFT) to study defects and functional groups present with the carbon fragments. Our calculations show that oxygen-, and nitrogen-containing defects are energetically favorable to form on one single layer carbon fragment (i.e. graphene) surfaces, and that the adsorption of oxygen functional groups on the graphene basal plane is favored as well. The effect of these defects and functional groups on metal storage was found to be highly beneficial, with Li, Na, and K adsorption energies greatly improved as compared to the pristine graphene surface. Hence, it was deduced that the presence of surface defects could indeed lead to a higher degree of metal storage, as has been postulated experimentally. The effect of these defects on metal migration, which would influence the anode materials cycling properties, was investigated through nudged elastic band calculations. Comparing the metal energy migration barriers on the defective surface to the pristine, it was concluded that, even though these defects are highly beneficial for metal storage, they are detrimental to metal migration. From defect formation energy calculations, it was seen that the defect expected to be present in the highest concentration on the carbon surface under equilibrium conditions is the 2OCNC defect, where three adjacent carbon have been substituted for two oxygen, and one nitrogen, respectively. This defect further has metal migration energy barriers many times higher than the corresponding ones at pristine surfaces, and would be highly detrimental for metal diffusion.12 We have also made efforts to model a more complex, disordered hard carbon structure. Metal intercalation energy as a function of carbon interlayer distance, cell voltage, and charge transfer of Na, Li, and K were calculated. It was seen that the defect formation energies calculated for graphene were further replicated in the carbon layers. Metal migration in the disordered structure showed metal migration energy barriers close to those observed by our experimental collaborators for sodiated hard carbons. This paper will also report our most recent study on the interactions of different electrolytes with the carbon surface, to understand the effects of electrolytes on the solid electrolyte interface. AcknowledgmentsThe financial support from EPSRC (Engineering and Physical Sciences Council) under the grant number (EP/M027066/1, EP/P003354/1, EP/R021554/1) is acknowledged. References 1 M.S. Balogun, Y. Luo, W. Qiu, P. Liu, and Y. Tong, Carbon N. Y. 98, 162 (2016). 2 M.D. Slater, D. Kim, E. Lee, and C.S. Johnson, Adv. Funct. Mater. 23, 947 (2013). 3 D.A. Stevens and J.R. Dahn, J. Electrochem. Soc. 148, A803 (2001). 4 J.C. Pramudita, D. Sehrawat, D. Goonetilleke, and N. Sharma, Adv. Energy Mater. 1602911, 1 (2017). 5 Z. Tai, Q. Zhang, Y. Liu, H. Liu, and S. Dou, Carbon N. Y. 123, 54 (2017). 6 Z. Jian, Z. Xing, C. Bommier, Z. Li, and X. Ji, Adv. Energy Mater. 6, 1 (2016). 7 E. Irisarri, A. Ponrouch, and M.R. Palacin, J. Electrochem. Soc. 162, A2476 (2015). 8 P. Lu, Y. Sun, H. Xiang, X. Liang, and Y. Yu, Adv. Energy Mater. 8, 1 (2018). 9 A. Hashimoto, K. Suenaga, A. Gloter, K. Urita, and S. Iijima, Nature 430, 870 (2004). 10 J. Kotakoski, A. V. Krasheninnikov, U. Kaiser, and J.C. Meyer, Phys. Rev. Lett. 106, 1 (2011). 11 Z. Ju, P. Li, G. Ma, Z. Xing, Q. Zhuang, and Y. Qian, Energy Storage Mater. 11, 38 (2018). 12 E. Olsson, G. Chai, M. Dove, Q. Cai, Nanoscale, under review.

Crystalline network form of Gefitinib molecule stabilized by non–covalent interactions: DFT–D calculations

The crystalline network of a stable form of Gefitinib (C22H24ClFN4O3) as a new anticancer has been theoretically studied. DFT calculations demonstrated that the packed network of Gefitinib was constructed by hydrogen bonds as the main constructor force. Hydrogen bond interactions link the molecular layers result to 2D structure formation along the bc plane of unit cell. However, network grows through π–stacking of the fragments along a direction. Dispersion corrected density functional theory calculations (DFT−D) were applied for evaluation of the binding energy value of the non–covalent forces which demonstrate NH⋯O and CH⋯O as the primary creator interactions of the intended 3D network. Moreover, the intermolecular HBs and π⋯stacking interactions were studied by Bader’s theory of AIM. Calculated/FP-LAPW visible region of optical spectra was shown that this molecule is approximately transparent in the x and z directions with greater interacting power in the z-direction than x and y ones. The maximum absorption is related to the x direction and it is low in the y and z directions because of the hydrogen bonds existence in bc plan.

Thermodynamic stability of hexagonal and rhombohedral boron nitride under chemical vapor deposition conditions from van der Waals corrected first principles calculations

Thin films of boron nitride (BN), particularly the sp2-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN), are interesting for several electronic applications, given the bandgaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400–1800 K and 1000–10 000 Pa, respectively. In this letter, the authors use the van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. The authors find that r-BN is the stable sp2-hybridized phase at CVD conditions, while h-BN is metastable. Thus, their calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

Interaction of different types of nanocages (Al12N12, Al12P12, B12N12, Be12O12, Mg12O12, Si12C12 and C24) with HCN and ClCN: DFT, TD-DFT, QTAIM, and NBO calculations

In this work, the ability of different types of nanocages including Al12N12, Al12P12, Be12O12, B12N12, Si12C12, Mg12O12 and C24 for the adsorption and detection of poisonous gases HCN and ClCN has been investigated, theoretically using the D3 dispersion corrected density functional theory (DFT-D3). The absorption spectra of HCN–nanocage and ClCN–nanocage complexes were calculated by the time-dependent density functional theory (TD-DFT) and compared with the calculated absorption spectrum of isolated nanocage to investigate the ability of nanocage for sensing of HCN and ClCN gases. It was found that the strongest interaction between HCN (ClCN) molecule and nanocage takes place when the molecule is adsorbed via its N atom on the surface of nanocage except for C24. Also, it was shown that the Al12N12 is the best adsorbent for HCN and ClCN gases among the selected nanocages and Si12C12 is the best sensor for the detection of these gases using the electroconductivity and absorption spectroscopy techniques.

The role of isotropic and anisotropic Hubbard corrections for the magnetic ordering and absolute band alignment of hematite α-Fe2O3(0001) surfaces

An isotropic (+U) and anisotropic [+(U−J)] corrected Density Functional Theory study for bulk hematite (α-Fe2O3) was carried out, and several competing terminations of its (0001) surface modeled via slabs of increasing thickness from twelve to thirty-six Fe-layers. In spite of small quantitative differences, the use of either U or (U-J) corrections showed not to qualitatively affect the results of the simulations both for bulk α-Fe2O3 and the lowest-energy α-Fe2O3(0001) surface studied, regardless of the thickness of the slab used. The energy favored antiferromagnetic ordering of bulk α-Fe2O3 was preserved in the relaxed slabs, with the largest surface-induced effects limited to the outermost three Fe-layers in the slabs. Mixed O- and Fe-terminations were found to be energetically favored and insulating. Conversely, fully O- or Fe-terminated surfaces were calculated to be energetically disfavored and metallic. Finally, the role of Fe- or O- termination for the semiconducting or metallic nature as well as absolute band alignment of α-Fe2O3(0001) surfaces was analyzed and discussed with respect to the challenges in enhancing the activity of α-Fe2O3 samples as photo-electrode for water splitting.

Adsorption of phosgene on Si-embedded MoS2 sheet and electric field-assisted desorption: insights from DFT calculations

In quest of effective materials and technologies for detecting toxic gas molecules, an attempt is made to detect phosgene gas molecule using MoS2 by employing dispersion corrected density functional theory calculations. Doping Si into the S-vacancy of MoS2 monolayer results in improvement of adsorption capability of phosgene gas molecule, reaching adsorption energy of − 1.228 eV. It is revealed that Si-doped MoS2 sheet is thermodynamically stable at high temperatures, and hence, room temperature stability is expected. Origin of interaction between phosgene and adsorbent is analyzed by calculating density of states, charge transfer, and vibrational frequency. Strong binding and more charge transfer modulate band gap and work function of the Si-doped MoS2 material post-phosgene adsorption indicate that such system is highly sensitive to phosgene. It is further shown that the sensing material is completely recovered by applying 0.6 V/A magnitude vertical positive electric field. The reason for reduced stability of the system is revealed by variations in charge transfer process and induced dipole interaction due to the charge redistribution. The results suggest potential application of MoS2-based sheets for sensing phosgene gas molecule, where external electric field efficiently aids reversible adsorption process.

Epitaxial Graphene Sensors Combined with 3D-Printed Microfluidic Chip for Heavy Metals Detection.

In this work, we investigated the sensing performance of epitaxial graphene on Si-face 4H-SiC (EG/SiC) for liquid-phase detection of heavy metals (e.g., Pb and Cd), showing fast and stable response and low detection limit. The sensing platform proposed includes 3D-printed microfluidic devices, which incorporate all features required to connect and execute lab-on-chip (LOC) functions. The obtained results indicate that EG exhibits excellent sensing activity towards Pb and Cd ions. Several concentrations of Pb2+ solutions, ranging from 125 nM to 500 µM, were analyzed showing Langmuir correlation between signal and Pb2+ concentrations, good stability, and reproducibility over time. Upon the simultaneous presence of both metals, sensor response is dominated by Pb2+ rather than Cd2+ ions. To explain the sensing mechanisms and difference in adsorption behavior of Pb2+ and Cd2+ ions on EG in water-based solutions, we performed van-der-Waals (vdW)-corrected density functional theory (DFT) calculations and non-covalent interaction (NCI) analysis, extended charge decomposition analysis (ECDA), and topological analysis. We demonstrated that Pb2+ and Cd2+ ions act as electron-acceptors, enhancing hole conductivity of EG, due to charge transfer from graphene to metal ions, and Pb2+ ions have preferential ability to binding with graphene over cadmium. Electrochemical measurements confirmed the conductometric results, which additionally indicate that EG is more sensitive to lead than to cadmium.

Structure of Electronically Reduced N-Donor Bidentate Ligands and Their Heteroleptic Four-Coordinate Zinc Complexes: A Survey of Density Functional Theory Results.

The role of Hartree-Fock exchange in describing the structural changes occurring upon reduction of bipyridine-based ligands and their complexes is investigated within the framework of density functional theory (DFT) calculations. A set of four free ligands in their neutral and radical anionic forms, and two of their zinc complexes in their dicationic and monocationic radical forms, is used to compare a large panel of pure, conventional, and long-range corrected hybrid DFT functionals; coupled cluster single and double calculations are used alongside experimental results as benchmarks. Particular attention has been devoted to the magnitude of the change, upon reduction, of the Δ-parameter, which measures the difference between the Cpy-Cpy and the C-N bond lengths in bipyridine ligand and is known to experimentally correlate with the charge of the ligands. Our results indicate that the structural changes significantly depend on the amount of exact exchange included in the functional. A progressive evolution is observed for the free ligands, whereas two distinct sets of results are obtained for the complexes. Functionals with a small degree of HF exchange, e.g., B3LYP, do not adequately describe geometric changes for the considered species, and, quite surprisingly, the same holds for the CC2 method. The best agreement to experimental and CCSD values is obtained with functionals that include a significant but not excessive part of exact exchange, e.g., CAM-B3LYP, M06-2X, and ωB97X-D. The calculated localization of the added electron after reduction, which depends on the self-interaction error, is used to rationalize these outcomes. Static correlation is also shown to play a role in the accurate description of the electronic structure.

Negative linear compressibility and structural phase transition in energetic silver azide under pressure: A first principles study

In this work, we have investigated high pressure behavior of silver azide within the framework of dispersion corrected density functional theory. We have predicted a pressure induced first order structural phase transition from orthorhombic (Ibam) → tetragonal (I4∕mcm) phase at 3.1 GPa. Ambient phase exhibits negative linear compressibility along a-axis in agreement with the experiments. Calculated phonon dispersion relations confirm the dynamical stability of ambient and high pressure phases. We have also analyzed bonding nature of alkali and transition metal azides, this provides an insight on possible correlation between structure-bonding-stability. The bonding nature between metal and terminal nitrogen of azide plays a predominant role in determining the order of stability in inorganic metal azides.

Thermal conductivity and diffusion mechanisms of noble gases in uranium dioxide: A DFT+U study

The bulk properties of uranium dioxide (UO2) have been investigated using Hubbard corrected density functional theory (DFT + U) calculations. Monitoring of the occupation matrix for 5f electrons of the uranium atoms is found to be crucial to avoid metastable state solutions and consequently to obtain the true ground state properties of bulk UO2. The lattice contribution to the thermal conductivity was obtained by the solution of the Boltzmann transport equation for phonons based on the interatomic force constants obtained from DFT + U calculations. Furthermore, the relative stabilities of noble gases (He, Ne, Ar, Kr, and Xe) in the octahedral interstitial site of bulk UO2 and their migration are revisited. The effect of the supercell approach for point defects is taken into account by considering the long-range elastic interactions. The computed incorporation energies and energy barriers indicate a size-dependent mechanism for the interstitial migration of noble gases.

Stretched or noded orbital densities and self-interaction correction in density functional theory.

Semilocal approximations to the density functional for the exchange-correlation energy of a many-electron system necessarily fail for lobed one-electron densities, including not only the familiar stretched densities but also the less familiar but closely related noded ones. The Perdew-Zunger (PZ) self-interaction correction (SIC) to a semilocal approximation makes that approximation exact for all one-electron ground- or excited-state densities and accurate for stretched bonds. When the minimization of the PZ total energy is made over real localized orbitals, the orbital densities can be noded, leading to energy errors in many-electron systems. Minimization over complex localized orbitals yields nodeless orbital densities, which reduce but typically do not eliminate the SIC errors of atomization energies. Other errors of PZ SIC remain, attributable to the loss of the exact constraints and appropriate norms that the semilocal approximations satisfy, suggesting the need for a generalized SIC. These conclusions are supported by calculations for one-electron densities and for many-electron molecules. While PZ SIC raises and improves the energy barriers of standard generalized gradient approximations (GGAs) and meta-GGAs, it reduces and often worsens the atomization energies of molecules. Thus, PZ SIC raises the energy more as the nodality of the valence localized orbitals increases from atoms to molecules to transition states. PZ SIC is applied here, in particular, to the strongly constrained and appropriately normed (SCAN) meta-GGA, for which the correlation part is already self-interaction-free. This property makes SCAN a natural first candidate for a generalized SIC.

Crystalline network study of new N-phthaloyl-β-Alanine with benzimidazole, cocrystal: Computational consideration & free radical scavenging activity

The new cocrystal adducts of N-phthaloyl-β-alanine and benzimidazole (1:2) with molecular formula C18H15N3O4 (1) was synthesized by slow evaporation process of the aqueous solution containing the two said moieties. The confirmation of proposed formula can be established through crystal structure as well as FTIR analysis. The crystal structure was confirmed by single X–ray crystal analysis. The experimental and theoretical studies of photophysical properties like Fourier Transform Infrared (FTIR) and ultraviolet–visible spectroscopy (UV–Vis) have been done. The cocrystal belong to monoclinic crystallographic system with space group P21/c, Z = 4. DPPH radical scavenging activity of the title cocrystal is slightly lower than coformer with lower IC50 value, respectively. One dimensional infinite chain in direction of [010] parallel to b direction. Optimized crystalline network structure of 1 shows that conventional N−H⋯O, and OH⋯N, and the non−conventional CH⋯O hydrogen bonds (HBs) gathered the monomeric components of 1 (1−mon). The reliable calculations of the dispersion corrected density functional theory (DFT−D) display that N−H⋯O and O−H⋯N HBs more share in the stabilization of the network structure. The theoretical study of UV–Vis spectra in solvents (water, acetonitrile, methanol, and n–heptanes) confirms the experimental results as seven main bands in 180–270 nm range. They could attribute to intra-ligand charge transfer (ILCT) as benzimidazole → benzimidazole and N-phthaloyl-β-alanine → N-phthaloyl-β-alanine with π → π* character.

Nonbonding interaction analyses on PVDF/[BMIM][BF4] complex system in gas and solution phase.

The present study provides a detailed quantum chemical description of the physicochemical interactions between poly-vinylidene fluoride (PVDF) and 1-butyl-3-methyl-imidazolium tetrafluoro borate ([BMIM][BF4]) ionic liquid (IL). Geometry optimization and frequency calculations are carried out for four monomer units of α- and β-PVDF, [BMIM][BF4], and PVDF/[BMIM][BF4] using dispersion corrected density functional theory. The effects of solvation on the systems under study are demonstrated for three polar aprotic solvents, namely tetra-hydrofuran (THF), acetone, and n,n-dimethyl formamide (DMF) using the integral equation formalism polarizable continuum model (IEFPCM). Calculated negative solvation free energy values suggest solution phase stability of the systems under study. Binding and interaction energies for β-PVDF/IL are found higher in magnitude than those for α-PVDF/IL. The nonbonding interaction phenomenon of β-PVDF/[BMIM][BF4] is elucidated on the basis of natural bond orbital (NBO), Bader's quantum theory of atoms in molecules (QTAIM), delocalization indices, Hirshfeld surface, and reduced density gradient (RDG) analyses. Both anions and cations of ionic liquids are found to show weak van der Waals interaction with PVDF molecule but the anion ([BF4]-)/PVDF interaction is found to be stronger than cation ([BMIM]+)/PVDF interaction. Inter-unit C-H⋯F type hydrogen bonds are found to show improper (causing blue shifts in vibrational frequencies) nature. Frontier molecular orbital analysis is carried out, and different chemical parameters like electronegativity, chemical potential, chemical hardness and softness, and electrophilicity index are calculated using Koopmans' theorem. Thermochemical calculations are also performed, and the variation in different standard thermodynamic parameters with temperature is formulated. Graphical abstract (a) Hirshfeld surface mapped onto electron density and (b) NCI isosurfaces showing inter-unit interactions of β-PVDF/[BMIM][BF4].

The Fragment Molecular Orbital Method Based on Long-Range Corrected Density-Functional Tight-Binding.

The presently available linear scaling approaches to density-functional tight-binding (DFTB) based on the fragment molecular orbital (FMO) method are severely impacted by the problem of artificial charge transfer due to the self-interaction error (SIE), which hampers the simulation of zwitterionic systems such as biopolymers or ionic liquids. Here we report an extension of FMO-DFTB where we included a long-range corrected (LC) functional designed to mitigate the DFTB SIE, called the FMO-LC-DFTB method, resulting in a robust method which succeeds in simulating zwitterionic systems. Both energy and analytic gradient are developed for the gas phase and the polarizable continuum model of solvation. The scaling of FMO-LC-DFTB with system size N is shown to be almost linear, O( N1.13-1.28), and its numerical accuracy is established for a variety of representative systems including neutral and charged polypeptides. It is shown that pair interaction energies between fragments for two mini-proteins are in excellent agreement with results from long-range corrected density functional theory. The new method was employed in long time scale (1 ns) molecular dynamics simulations of the tryptophan cage protein (PDB: 1L2Y ) in the gas phase for four different protonation states and in stochastic global minimum structure searches for 1-ethyl-3-methylimidazolium nitrate ionic liquid clusters containing up to 2300 atoms.