Corrected Density Functional Theory Research Articles

Roles of Singlet Fission in the Photosensitization of Silicon Phthalocyanine.

The roles of singlet fission in the triplet generation of silicon phthalocyanine (SiPc), a compound analogous to the IRDye700DX photosensitizer used in near-infrared photoimmunotherapy, are investigated by considering the energetical relation between the excitations of this compound. These excitations are obtained through spin-flip long-range corrected time-dependent density functional theory calculations. To initiate singlet fission, chromophores must meet two conditions: (1) near-degenerate low-lying singlet and quintet (triplet-triplet) excitations with a considerable energy gap of the lowest singlet and triplet excited states and (2) moderate π-stacking energy of chromophores, which is higher than but not far from the solvation energy, to facilitate the dissociation and generation of triplet-state chromophores. The present calculations demonstrate that SiPc satisfies both of these conditions after the formation of π-stacking irrespective of the presence of an axial ligand(s), suggesting that singlet fission plays a crucial role in the triplet generation process, although intersystem crossing occurs simultaneously at a very slow rate.

Computational design of efficient corannulene-based Non-Fullerene acceptors for organic solar cells applications

In our study, we aimed to enhance the optoelectronic properties of corannulene through functionalization for use as a non-fullerene acceptor (NFA) in organic solar cells. To achieve this, we designed new corannulene derivatives by introducing various electron-donating and electron-withdrawing groups onto the corannulene core. Geometric, electronic, optical, and charge transport properties of newly designed molecules are analyzed using long-range corrected density functional theory methods. The potential NFA is identified by conducting extensive analysis, such as light absorption properties, ground-state dipole moments, and the energy difference between LUMO and LUMO+1 orbitals. Also, a model donor–acceptor interface is constructed by considering PTQ10 oligomer as the donor and corannulene derivatives as acceptors. Charge-transfer states and exciton dissociation processes are analyzed at the polymer chain and NFA interface. Overall, the results obtained from this study can provide useful guidance in designing high-performing NFAs.

Corrected density functional theory and the random phase approximation: Improved accuracy at little extra cost.

We recently introduced an efficient methodology to perform density-corrected Hartree-Fock density functional theory [DC(HF)-DFT] calculations and an extension to it we called "corrected" HF DFT [C(HF)-DFT] [Graf and Thom, J. Chem. Theory Comput. 19 5427-5438 (2023)]. In this work, we take a further step and combine C(HF)-DFT, augmented with a straightforward orbital energy correction, with the random phase approximation (RPA). We refer to the resulting methodology as corrected HF RPA [C(HF)-RPA]. We evaluate the proposed methodology across various RPA methods: direct RPA (dRPA), RPA with an approximate exchange kernel, and RPA with second-order screened exchange. C(HF)-dRPA demonstrates very promising performance; for RPA with exchange methods, on the other hand, we often find over-corrections.

First-principles study of structural, hydrogen bonds and mechanical properties of α-RDX under hydrostatic compression

The mechanical response of cyclotrimethylene trinitramine (RDX) under pressure loading is closely correlated with the structural deformation and chemical decomposition. The structural, hydrogen bonds (HBs) and mechanical properties of α-RDX under hydrostatic compression between 0 and 4 GPa have been studied using dispersion corrected density functional theory (DFT-D). The oxygen atoms in the E branch (AAE configuration) form important intermolecular HBs with pressure increasing, wherein the bond order of the HB marked as O3∙∙∙H5-C3 reaches up to 0.0716 (∼1.8 times of the intramolecular bonds) at 4 GPa. This HB directly prompts the pressure-dependent increase of Young’s modulus in y direction. α-RDX keeps mechanically stable below 4 GPa, while it shows a pressure-induced ductility owing to deformation tendency in (010) plane (i.e., ac plane). Finally, the pressure-dependent anisotropy, sound velocities and Debye temperature are also discussed based on the calculated mechanical moduli.

Combined density functional theory and molecular dynamics analyses on Lithium/Sodium ion interaction and diffusion in gel polymer electrolytes with poly-vinylidene fluoride scaffold, propylene carbonate/Ionic Liquid solvent, and perchlorate salt

Choice of a proper electrolyte is very crucial to enhance the overall performance of a metal-ion battery. In this work, dispersion corrected density functional theory and classical molecular dynamics simulations are carried out to explore the metal ion (Li+ and Na+) interaction and diffusion through polyvinylidene fluoride (PVDF)-based gel polymer electrolytes. Four types of polymer/solvent/salt electrolyte systems are investigated considering PVDF scaffold for each case, and conventionally used propylene carbonate and rarely used, albeit cheaper, ionic liquid [BMIM][ClO4] as solvent, along with metal perchlorate salts LiClO4 and NaClO4. Inter-unit interactions within the electrolyte clusters, electrolyte uptake, and electrochemical stability of the electrolytes are explained by gas-phase DFT analyses, considering the polymer/solvent/salt components in 1:1:1 molecular ratio. Diffusion of the ions and ionic conductivity of the electrolytes are explored by MD simulation referring to two different size and time scales. From the DFT-based non-bonding interaction analyses, metal ions are found to exhibit strong non-covalent interactions with the adjacent O and F atoms, where the O atoms are parts of PC and [ClO4]- ions, and F atoms are from the PVDF chains. [BMIM]+, [ClO4]-, and PVDF are found to interact through weak van der Waals type hydrogen bonds. Both DFT and MD calculations suggest that, Li+ and Na+ ions are primarily coordinated with [ClO4]- ions. Dynamics studies confirm that for PVDF/IL/salt, total ionic conductivity is predominated by [BMIM]+ and [ClO4]-, exhibiting lower metal ion diffusivity as compared to PC-containing electrolytes. For both Li- and Na-ion systems, owing to the availability of higher number of charge carriers, electrolytes containing ILs show higher ionic conductivity compared to those containing PC as the solvent.

Density-Corrected Density Functional Theory for Open Shells: How to Deal with Spin Contamination.

Density functional theory (DFT) is usually used self-consistently to predict chemical properties, but the use of the Hartree-Fock (HF) density improves energetics in certain, well-characterized cases. Density-corrected (DC) DFT provides the theory behind this, but unrestricted Hartree-Fock (UHF) densities yield poor energetics in cases of strong spin contamination. Here we compare with restricted open-shell HF (ROHF) across 13 different functionals and two DC-DFT methods. For significant spin contamination, ROHF densities outperform UHF densities by as much as a factor of 3, depending on the energy functional, and ROHF-DFT improves over self-consistent DFT for most of the tested functionals. We refine the DC(HF)-DFT algorithm to use ROHF densities in cases of severe spin contamination.

Diamine-appended metal-organic framework for carbon capture from wet flue gas: Characteristics and mechanism

Due to the superior CO2 adsorption capacity and selectivity, amine-functional solid adsorbents have received increasing attention. Nevertheless, amine-functionalized polyporous materials have a large performance deviation when considering carbon removal capacity under wet flue gas. Therefore, a variety of metal–organic frameworks (MOFs) with amine functionality are synthesized in this work by appending diamine with a propylene linker to Mg2(dobpdc) (dobpdc4- = 4,4′-dioxido-3,3′-biphenyldicarboxylate) and screened under the simulated flue gas environment with a high water content (7 v%). The results indicate that ndmpn-grafted Mg2(dobpdc) (ndmpn = N,N-dimethyl-1,3-propanediamine) has a high CO2 adsorption capacity of 1.72 mmol/g at 60 °C with an extremely low regeneration heat (2.26 GJ/ton CO2 at the desorption temperature of 145 °C). Adsorption property of ndmpn-Mg2(dobpdc) at high humidity is even more excellent than that of another well-reported diaminopropene-appended MOF, dmpn-Mg2(dobpdc) (dmpn = 2,2-dimethyl-1,3-propanediamine). Herein, van der Waals (vdW)-corrected density functional theory (DFT) calculations are used to quantitatively analyze binding strengths and water effects on it between diamine-appended Mg2(dobpdc) and CO2. It is revealed that the addition of water makes ammonium carbamate chains produced in ndmpn-Mg2(dobpdc) more stable. These chemisorption structures under humid conditions have also been disclosed by using 15N solid-state nuclear magnetic resonance (NMR) spectroscopy experiments and DFT calculation. To conclude, we unveil the binary adsorption characteristics and mechanism of ndmpn-Mg2(dobpdc). It enables a thorough understanding of this compound and highlights its potential as a promising adsorbent under humid conditions for post-combustion applications.

Electrochemical properties of endohedral halide (F−, Cl− and Br−) encapsulated Mg12O12 nanocage for metal-ion batteries

Metal-ion batteries (MIBs) offer great potential for energy storage applications due to their advantageous features such as high energy density and environmental friendliness. Nevertheless, there is a need to investigate electrode materials that possess attributes like substantial capacity, rapid charge and discharge capabilities, stable performance over numerous cycles, and cost-effectiveness. In this context, the effectiveness of pristine and halide (F−, Cl− and Br−) encapsulated Mg12O12 nanocages are systematically examined and employed as anode materials for metal-ion batteries. Using dispersion corrected density functional theory (DFT-D3), the electrochemical performance of the nanocages in the presence and absence of halide were investigated. The oxygen atom of Mg12O12 nanocages prefers to adsorb on M/M+ (M = Li, Na, and K). The results show that, on comparison to neutral metal, cationic metal have stronger interaction for both pristine and halide encapsulated nanocages. The computed Gibbs free energy of the cell (ΔGcell) and cell voltage (Vcell) of pristine Mg12O12 adsorption of alkali metals for MIBs are found to be in the range of −13.18 to −38.91 kcal/mol and 0.57 to 1.69 V respectively. Endohedral encapsulation of the halide into the nanocages significantly increased the Gibbs free energy, which subsequently enhanced the cell voltage of the nanocages. The findings imply that Mg12O12 nanocage with halide encapsulation acts as an effective anode material for MIBs with profound performance. The outcomes of this investigation pave the way for the development of novel approaches in designing both pristine and halide (F−, Cl−, and Br−) encapsulated Mg12O12 nanocages as anodes, thereby facilitating their practical utilization in metal-ion batteries.

The influence of Co nucleation in Co[sbnd]Ni single atom alloy on low-temperature methane dry reforming with DFT simulations and microkinetic modeling

CO2 reacting with CH4 to produce value-added syngas CO and H2 is an attractive approach to utilize CO2 and achieve carbon neutralization. The present work employed the dispersion corrected density functional theory (DFT) and microkinetic modeling to investigate the influence of Co nucleation in CoNi single atom alloy (SAA) on low-temperature methane dry reforming (DRM). It is found that the Co nucleation in CoNi SAA did not alter the most favorable reaction path. That is, CH4 is dehydrogenated to CH* step by step, then CH* is oxidized by O* from CO2 direct decomposition to obtain CHO*, and finally CHO* is dehydrogenated to produce CO. For the decomposition of CO2, the direct decomposition of CO2 prefers over the assisted decomposition of CO2 by H* via COOH* or HCOO* intermediates decomposition to obtain the final product CO. Microkinetic modeling results reveal that the nucleation of single Co atoms to Co dimer or a surface Co layer favors the conversion of methane and CO2 at 773 K but reduces the coke-resistance ability. Reverse water-gas shift does not change the key species on the surface but interferes the product distribution and surface rate-limiting step.

First‐principles Assessment of the Role of Water in the Reduction Half Cycle of Low‐Temperature NH3‐SCR over Cu‐CHA

AbstractDispersion corrected density functional theory calculations show that the presence of H2O in the Reduction Half‐Cycle (RHC) of NH3‐SCR affects the free energy of the kinetically‐relevant transition state (TS) leading to a reduction in the rate and activation energy with respect to dry conditions. In particular, H2O enthalpically stabilizes the kinetically‐relevant TS by 20 kJ mol−1 with respect to the dry counterpart. Such enthalpic stabilization vanishes when van der Waals (vdW) interactions are excluded from the calculations, thus showing the preeminent role of non‐specific dispersion forces in the reduction of the activation enthalpy. At the same time, the enthalpic stabilization is more than compensated by the additional entropy losses of the TS brought forth by the presence of H2O in the CHA cage. Calculated enthalpy and entropy changes with respect to the dry case agree quantitatively with the experimental measurements and reflect the modified reacting environment in the presence of H2O. As a result, this study provides theoretical underpinnings on the mechanistic role of H2O in the RHC and, on a more general basis, highlights the importance of the molecular scale description of the reaction environment in voids of molecular dimensions.

Adsorption of DNA nucleobases on single-layer Ti3C2 MXene and graphene: vdW-corrected DFT and NEGF studies.

We investigated the interaction of DNA nucleobases [adenine (A), guanine (G), thymine (T), and cytosine (C)] with single-layer Ti3C2 MXene using Van der Waals (vdW)-corrected density functional theory and non-equilibrium Green's function methods. All calculations were benchmarked against graphene. We showed that depending on the initial vertical height of a nucleobase above the Ti3C2 surface, two interaction mechanisms are possible, namely, physisorption and chemisorption. For graphene, DNA nucleobases always physisorbed onto the graphene surface irrespective of the initial vertical height of the nucleobase above the graphene sheet. The PBE+vdW binding energies for graphene are high (0.55-0.74eV) and follow the order G > A > T > C, with adsorption heights in the range of 3.16-3.22 Å, indicating strong physisorption. For Ti3C2, the PBE+vdW binding energies are relatively weaker (0.16-0.20eV) and follow the order A > G = T > C, with adsorption heights in the range of 5.51-5.60 Å, indicating weak physisorption. The binding energies for chemisorption follow the order G > A > T > C, which is the same order for physisorption. The binding energy values (5.3-7.5eV) indicate very strong chemisorption (∼40 times larger than the physisorption binding energies). Furthermore, our band structure and electronic transport analysis showed that for physisorption, there is neither significant variation in the band structure nor modulation in the transmission function and device density of states. The relatively weak physisorption and strong chemisorption show that Ti3C2 might not be capable of identifying DNA nucleobases using the physisorption method.

Simple and Efficient Route toward Improved Energetics within the Framework of Density-Corrected Density Functional Theory.

The crucial step in density-corrected Hartree-Fock density functional theory (DC(HF)-DFT) is to decide whether the density produced by the density functional for a specific calculation is erroneous and, hence, should be replaced by, in this case, the HF density. We introduce an indicator, based on the difference in noninteracting kinetic energies between DFT and HF calculations, to determine when the HF density is the better option. Our kinetic energy indicator directly compares the self-consistent density of the analyzed functional with the HF density, is size-intensive, reliable, and most importantly highly efficient. Moreover, we present a procedure that makes best use of the computed quantities necessary for DC(HF)-DFT by additionally evaluating a related hybrid functional and, in that way, not only "corrects" the density but also the functional itself; we call that procedure corrected Hartree-Fock density functional theory (C(HF)-DFT).

Pressure-induced transitions in FePS$_3$: Structural, magnetic and electronic properties

FePS_33 is a prototype van der Waals layered antiferromagnet and a Mott insulator under ambient conditions, which has been recently reported to go through a pressure-induced dimensionality crossover and an insulator-to-metal transition. These transitions also lead to the appearance of a novel magnetic metallic state. To further understand these emergent structural and physical properties, we have performed a first-principles study using van der Waals and Hubbard UU corrected density functional theory including a random structure search. Our computational study attempts to interpret the experimental coexistence of the low- and intermediate-pressure phases and we predict a novel high-pressure phase with distinctive dimensionality and different possible origins of metallicity.

Understanding the role of oxygen-vacancy defects in Cu2O(111) from first-principle calculations

The presence of defects, such as copper and oxygen vacancies, in cuprous oxide films determines their characteristic carrier conductivity and consequently their application as semiconducting systems. There are still open questions on the induced electronic re-distribution, including the formation of polarons. Indeed, to accurately reproduce the structural and electronic properties at the cuprous oxide surface, very large slab models and theoretical approaches that go beyond the standard generalized gradient corrected density functional theory are needed. In this work we investigate oxygen vacancies formed in proximity of a reconstructed Cu2O(111) surface, where the outermost unsaturated copper atoms are removed, thus forming non-stoichiometric surface layers with copper vacancies. We address simultaneously surface and bulk properties by modelling a thick and symmetric slab, to find that hybrid exchange-correlation functionals are needed to describe the oxygen vacancy in this system. Our simulations show that the formation of oxygen vacancies is favoured in the sub-surface layer. Moreover, the oxygen vacancy leads to a splitting and left-shift of the shallow hole states in the gap, which are associated with the deficiency of copper at the surface. These findings suggest that surface electronic structure and reactivity are sensitive to the presence of oxygen vacancies, also when the latter are formed deeper within the film.

Reversible hydrogen storage in Ti decorated small boron clusters: Insights from molecular dynamics simulations

We report the hydrogen adsorption capacity of Ti doped boron clusters (BnTi2, n = 6–10) using dispersion corrected density functional theory. The stability and the reactivity of the studied clusters were confirmed by their reactivity indices. It was shown that each titanium atom can accommodate up to 5H2 molecules with average adsorption energy falling in the range of 0.15–0.21 eV/H2 via Niu-Rao-Jena kind of interaction. An elongation in H–H bond length was found to be 0.76–0.80 Å with average Ti–H2 bond distance being 2.754 Å which confirmed molecular physisorption of H2. The molecular dynamics simulation demonstrated that, these clusters could adsorb all H2 molecules at low temperature (77K) while desorbing almost all the H2 molecules at 300K and 373K. The occupation number calculation revealed that these clusters could hold up to 10.20 wt % of H2 molecules at storage condition (100K-60bar).

Assignment of the absolute configuration of molecules that are chiral by virtue of deuterium substitution using chiral tag molecular rotational resonance spectroscopy.

Chiral tag molecular rotational resonance (MRR) spectroscopy is used to assign the absolute configuration of molecules that are chiral by virtue of deuterium substitution. Interest in the improved performance of deuterated active pharmaceutical ingredients has led to the development of precision deuteration reactions. These reactions often generate enantioisotopomer reaction products that pose challenges for chiral analysis. Chiral tag rotational spectroscopy uses noncovalent derivatization of the enantioisotopomer to create the diastereomers of the 1:1 molecular complexes of the analyte and a small, chiral molecule. Assignment of the absolute configuration requires high-confidence determinations of the structures of these weakly bound complexes. A general search method, CREST, is used to identify candidate geometries. Subsequent geometry optimization using dispersion corrected density functional theory gives equilibrium geometries with sufficient accuracy to identify the isomers of the chiral tag complexes produced in the pulsed jet expansion used to introduce the sample into the MRR spectrometer. Rotational constant scaling based on the fact that the diastereomers have the same equilibrium geometry gives accurate predictions allowing identification of the homochiral and heterochiral tag complexes and, therefore, assignment of absolute configuration. The method is successfully applied to three oxygenated substrates from enantioselective Cu-catalyzed alkene transfer hydrodeuteration reaction chemistry.

Density-Corrected Density Functional Theory for Molecular Properties.

Density-corrected (DC) density functional theory (DFT) has been proposed to overcome difficulties related to the self-interaction error. The procedure uses the Hartree-Fock electron density (matrix) non-self-consistently in conjunction with an approximate functional. DC-DFT has so far mainly been tested for total energy differences, whereas other types of molecular properties have not been evaluated systematically. This work focuses on the performance of DC-DFT for molecular properties, namely, dipole moments, static polarizabilities, and electric field gradients (EFGs) at atomic nuclei. Accurate reference data were generated from coupled-cluster theory to assess the performance of DC and self-consistent DFT calculations for twelve molecules, including diatomics with transition metals. DC-DFT does no harm in dipole moment calculations, but it negatively impacts the polarizability in at least one case. DC-DFT performs well for EFGs, even for the difficult case of CuCl.

Impact of Zr substitution on the electronic structure of ferroelectric hafnia

HfO2-based dielectrics are promising for nanoscale ferroelectric applications, and the most favorable material within the family is Zr-substituted hafnia, i.e., Hf1−xZrxO2 (HZO). The extent of Zr substitution can be great, and x is commonly set to 0.5. However, the bandgap of ZrO2 is lower than HfO2, thus it is uncertain how the Zr content should influence the electronic band structure of HZO. A reduced bandgap is detrimental to the cycling endurance as charge injection and dielectric breakdown would become easier. Another issue is regarding the comparison on the bandgaps between HfO2/ZrO2 superlattices and HZO solid-state solutions. In this work, we systematically investigated the electronic structures of HfO2, ZrO2, and HZO using self-energy corrected density functional theory. In particular, the conduction band minimum of Pca21-HfO2 is found to lie at an ordinary k-point on the Brillouin zone border, not related to any interlines between high-symmetry k-points. Moreover, the rule of HZO bandgap variation with respect to x has been extracted. The physical mechanisms for the exponential reduction regime and linear decay regime have been revealed. The bandgaps of HfO2/ZrO2 ferroelectric superlattices are investigated in a systematic manner, and the reason why the superlattice could possess a bandgap lower than that of ZrO2 is revealed through comprehensive analysis.

Charge Transport Properties of a Series of Metal Quinolates Utilising Dispersion-Corrected Density Functional Theory

The electronic and charge transport properties of Metal-Quinolates (Metal = Li, Na, K, Rb and Cs) compounds are theoretically investigated using AustinFrisch-Petersson functional with dispersion (APFD) corrected density functional theory (DFT). The calculated energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital ranges from 3.40 eV for LiQ to 0.93 eV for CsQ. The ionisation potential, electron affinity and chemical hardness of the compounds are calculated. We found that the electron hopping rate, kelectron of CsQ is around 150 times greater than LiQ. We suggest that CsQ is the most efficient charge injecting or transport material for organic light-emitting diodes (OLEDs). Dimer formation is desirable with all M-Quinolate with different electronic structures and (CsQ)2 dimer shows the lowest dimerisation energy.

Switchable Xe/Kr Selectivity in a Hofmann-Type Metal-Organic Framework via Temperature-Responsive Rotational Dynamics.

The development of adsorbents for Kr and Xe separation is essential to meet industrial demands and for energy conservation. Although a number of previous studies have focused on Xe-selective adsorbents, stimuli-responsive Xe/Kr-selective adsorbents still remain underdeveloped. Herein, a Hofmann-type framework Co(DABCO)[Ni(CN)4 ] (referred to as CoNi-DAB; DABCO = 1,4-diazabicyclo[2,2,2]octane) that provides a temperature-dependent switchable Xe/Kr separation performance is reported. CoNi-DAB showed high Kr/Xe (0.8/0.2) selectivity with significant Kr adsorption at 195K as well as high Xe/Kr (0.2/0.8) selectivity with superior Xe adsorption at 298K. Such adsorption features are associated with the temperature-dependent rotational configuration of the DABCO ligand, which affects the kinetic gate-opening temperature of Xe and Kr. The packing densities of Xe (2.886gcm-3 at 298K) and Kr (2.399g cm-3 at 195K) inside the framework are remarkable and comparable with those of liquid Xe (3.057gcm-3 ) and liquid Kr (2.413gcm-3 ), respectively. Breakthrough experiments confirm the temperature-dependent reverse separation performance of CoNi-DAB at 298K under dry and wet (88% relative humidity) conditions and at 195K under dry conditions. The unique adsorption behavior is also verified through van der Waals (vdW)-corrected density functional theory (DFT)calculations and nudged elastic band (NEB) simulations.