Dispersion Correction Scheme Research Articles

Investigating the molecular crystals of L-Alanine, DL-Alanine, β-Alanine, and Alanine hydrogen chloride: Experimental and DFT analysis of structural and optoelectronic properties

In this study, DFT calculations were employed to assess and contrast the structural, electronic, and optical characteristics of five alanine crystal forms. The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) with the Tkatchenko-Scheffler dispersion correction scheme was employed and compared to the PBE functional and the local density approximation (LDA) without dispersion correction. Experimentally, alanine crystal powders were characterized through X-ray diffraction (XRD) and UV–VIS absorption spectrum. Additionally, UV–VIS absorption measurements were performed on L-α-alanine, DL-alanine, β-alanine, and alanine hydrochloride solvated in water. Significant deviations (>10%) were observed between the experimental crystal lattice parameters and those predicted by the GGA and LDA methods. Incorporating dispersion correction into the GGA functional improved prediction accuracy. Additionally, time-dependent DFT (TD-DFT) computations using the polarizable continuum model were conducted to analyze the UV/VIS absorption spectrum of α-, β-, DL-, and hydrogen chloride alanine in water and interpret experimental data. Different alanine crystals exhibited substantial anisotropic electronic and optical properties, including effective masses, absorption, and dielectric function. The L-α-HCl structure displayed the smallest band gap (4.67 eV), suggesting its suitability for applications such as L-α/L-α-HCl/L-α quantum well structures. The main effective masses of electrons and holes were also determined for each crystal for a better understanding of their electronic transport properties.

Decoding energy decomposition analysis: Machine-learned Insights on the impact of the density functional on the bonding analysis.

The concept of chemical bonding is a crucial aspect of chemistry that aids in understanding the complexity and reactivity of molecules and materials. However, the interpretation of chemical bonds can be hindered by the choice of the theoretical approach and the specific method utilized. This study aims to investigate the effect of choosing different density functionals on the interpretation of bonding achieved through energy decomposition analysis (EDA). To achieve this goal, a data set was created, representing four bonding groups and various combinations of functionals and dispersion correction schemes. The calculations showed significant variation among the different functionals for the EDA terms, with the dispersion correction terms exhibiting the highest variability. More information was extracted by using machine learning in combination with dimensionality reduction on the data set. Results indicate that, despite the differences in the EDA terms obtained from different functionals, the functional has the least significant impact, suggesting minimal influence on the bonding interpretation.

Hydrogen storage in Sc-decorated Ψ-graphene via density functional theory simulations

Efficient methods and materials to store hydrogen onboard in light-duty fuel cell vehicles is crucial to move away from fossil fuels in the transport sector. Metal-decorated carbon materials are considered as promising materials for hydrogen storage. In this regard, using density functional theory (DFT) simulations incorporating the generalized gradient approximation functional along with the DFT-D2 dispersion correction scheme, we predict that Sc-decorated Ψ-graphene is a promising hydrogen storage material. The Sc atom binds strongly to Ψ-graphene (binding energy ∼3.02 eV), and binds seven H2, with an average binding energy of −0.36 eV/H2 and desorption temperature of ∼400 K. The hydrogen storage capacity with five and seven H2 is 8.59 and 14.46 wt%, respectively, which achieves the requirements of the U. S. Department of Energy for an efficient, onboard and reversible hydrogen storage material in light fuel cell vehicles. The system is stable at room temperature, as verified by ab initio molecular dynamics simulations. The likelihood of Sc–Sc clustering is low due to the high diffusion energy barrier of Sc over the Ψ-graphene surface. Thus, we predict that Sc-doped Ψ-graphene is an excellent reversible hydrogen storage material.

Common Cations Are Not Polarizable: Effects of Dispersion Correction on Hydration Structures from Ab Initio Molecular Dynamics.

We employed density functional theory-based ab initio molecular dynamics simulations to examine the hydration structure of several common alkali and alkali earth metal cations. We found that the commonly used atom pairwise dispersion correction scheme D3, which assigns dispersion coefficients based on the neutral form of the atom rather than its actual oxidation state, leads to inaccuracies in the hydration structures of these cations. We evaluated this effect for lithium, sodium, potassium, and calcium and found that the inaccuracies are particularly pronounced for sodium and potassium compared to the experiment. To remedy this issue, we propose disabling the D3 correction specifically for all cation-including pairs, which leads to a much better agreement with experimental data.

Modeling of Structure H Carbon Dioxide Clathrate Hydrates: Guest-Lattice Energies, Crystal Structure, and Pressure Dependencies.

We performed first-principles computations to investigate the complex interplay of molecular interaction energies in determining the lattice structure and stability of CO2@sH clathrate hydrates. Density functional theory computations using periodic boundary conditions were employed to characterize energetics and the key structural properties of the sH clathrate crystal under pressure, such as equilibrium lattice volume and bulk modulus. The performance of exchange–correlation functionals together with recently developed dispersion-corrected schemes was evaluated in describing interactions in both short-range and long-range regions of the potential. Structural relaxations of the fully CO2-filled and empty sH unit cells yield crystal structure and lattice energies, while their compressibility parameters were derived by including the pressure dependencies. The present quantum chemistry computations suggest anisotropy in the compressibility of the sH clathrate hydrates, with the crystal being less compressible along the a-axis direction than along the c-axis one, in distinction from nearly isotropic sI and sII structures. The detailed results presented here give insight into the complex nature of the underlying guest–host interactions, checking earlier assumptions, providing critical tests, and improving estimates. Such entries may eventually lead to better predictions of thermodynamic properties and formation conditions, with a direct impact on emerging hydrate-based technologies.

Dimethyl fumarate molecule, crystal, and plane: Optical absorption measurement and structural/optoelectronic properties by density functional theory calculations

Dimethyl fumarate (DMF) is the main fumaric acid ester of the Fumaderm advanced medicament for the treatment of psoriasis and multiple sclerosis. Many properties of the DMF molecule and its crystal are still unknown. Here, the structural, electronic, and optical properties of DMF in molecular form and in the form of triclinic van der Waals crystals are addressed within the framework of density functional theory (DFT) formalism. The computations were performed using local density and generalized gradient exchange-correlation functionals, LDA and GGA, respectively, including one dispersion correction scheme for the former and two for the latter. Besides, the Δ-sol correction method was applied to improve the band-gap energy estimated from the DFT computations. The UV/Vis spectra of the DMF molecule solvated in ethanol and in the crystal were measured and compared with theoretical data obtained from time-dependent DFT (molecule) and DFT (crystal) calculations. One of the dispersion-corrected GGA functionals achieved very accurate descriptions of the lattice parameters, while analysis of the Kohn–Sham band structure indicated that the DMF crystal has a direct band-gap energy of 3.12 eV, differing from the experimental band-gap (4.00 eV) by 0.88 eV. By applying the Δ-sol correction method, the band-gap energy increased to 3.95 eV, only 0.05 eV below the experimental value. Lastly, simulations were also carried out for a single DMF monolayer, for which a band-gap of 3.26 eV was predicted. Hence, intermolecular interactions tend to decrease the electronic energy gap according to the sequence Gapcrystal < Gapmonolayer < Gapmolecule.

Structural and Electronic Properties of SnO Downscaled to Monolayer.

Two-dimensional (2D) SnO is a p-type semiconductor that has received research and industrial attention for device-grade applications due to its bipolar conductivity and transparent semiconductor nature. The first-principles investigations based on the generalized gradient approximation (GGA) level of theory often failed to accurately model its structure due to interlayer Van der Waals interactions. This study is carried out to calculate structural and electronic properties of bulk and layered structures of SnO using dispersion correction scheme DFT+D3 with GGA-PBE to deal with the interactions which revealed good agreement of the results with reported data. The material in three-dimensional bulk happened to be an indirect gap semiconductor with a band gap of 0.6 eV which is increased to 2.85 eV for a two-dimensional monolayer structure. The detailed analysis of the properties demonstrated that the SnO monolayer is a promising candidate for future optoelectronics and spintronics devices, especially thin film transistors.

Nanoscale MXene Interlayer and Substrate Adhesion for Lubrication: A Density Functional Theory Study.

Understanding the interlayer interaction at the nanoscale in two-dimensional (2D) transition metal carbides and nitrides (MXenes) is important to improve their exfoliation/delamination process and application in (nano)-tribology. The layer–substrate interaction is also essential in (nano)-tribology as effective solid lubricants should be resistant against peeling-off during rubbing. Previous computational studies considered MXenes’ interlayer coupling with oversimplified, homogeneous terminations while neglecting the interaction with underlying substrates. In our study, Ti-based MXenes with both homogeneous and mixed terminations are modeled using density functional theory (DFT). An ad hoc modified dispersion correction scheme is used, capable of reproducing the results obtained from a higher level of theory. The nature of the interlayer interactions, comprising van der Waals, dipole–dipole, and hydrogen bonding, is discussed along with the effects of MXene sheet’s thickness and C/N ratio. Our results demonstrate that terminations play a major role in regulating MXenes’ interlayer and substrate adhesion to iron and iron oxide and, therefore, lubrication, which is also affected by an external load. Using graphene and MoS2 as established references, we verify that MXenes’ tribological performance as solid lubricants can be significantly improved by avoiding −OH and −F terminations, which can be done by controlling terminations via post-synthesis processing.

Ionic Dynamics and Vibrational Spectral Diffusion of a Protic Alkylammonium Ionic Salt through Intrinsic Cationic N-H Vibrational Probe from FPMD Simulations.

We employed density functional theory (DFT)-based molecular dynamics simulations to explore the structure, dynamics, and spectral properties of the protic ionic entity trimethylammonium chloride (TMACl). Structural investigations include calculating the site-site radial distribution functions (RDFs), the distribution of constituent cations and anions in three-dimensional space, and combined distribution functions of the hydrogen-bonded pair RDF versus angle, revealing the structural characteristics of the ionic solvation and the intermolecular interactions within ions. Further, we determined the instantaneous vibrational stretching frequencies of the intrinsic N-H stretch probe modes by applying the time-series wavelet method. The associated ionic dynamics within the protic ionic compound were investigated by calculating the time-evolution of the fluctuating frequencies and the frequency-time correlation functions (FFCFs). The time scale related to the local structural relaxation process and the average hydrogen bond lifetime, ion cage dynamics, and mean squared displacement were investigated. The faster decay component of the FFCFs, depicting the intermolecular motion of intact hydrogen bonds in TMACl, is 0.07 ps for the Perdew-Burke-Ernzerhof (PBE)-based simulation and 0.06 ps for the PBE-D2 representation. The slower time scale of the longer picosecond decay time component of PBE and PBE-D2 representations are 3.13 and 2.87 ps, respectively. These picosecond time scales represent more significant fluctuations of the hydrogen-bonding partners in the ionic entity and hydrogen-bond jump events accompanied by large angular jumps. The longest picosecond time scales represent structural relaxation, including large angular jumps and ion-pair dynamics. Also, ion cage lifetimes correlate with the slowest time scale of the associated dynamics of vibrational spectral diffusion despite the type of DFT functional. This study benchmarks DFT treatments of the exchange-correlation functional with and without the van der Waals (vdW) dispersion correction scheme. The inclusion of vdW interactions to the PBE functional represents a less structured state of the ionic entity and faster dynamics of the molecular motions relative to the one predicted by the PBE system. All the results illustrate the necessity of accurately describing the Coulomb interactions, vdW dispersive interactive forces, and localized hydrogen bonds required to sustain the energetic balance in this ionic salt.

Optical absorption measurements and optoelectronic DFT calculations for ethanol solvated quercetin and anhydrous/hydrated quercetin crystals

UV–vis optical absorption measurements of the ethanol solvated quercetin molecule and the dihydrate triclinic quercetin crystal were performed, as well as the electronic structure of the ethanol solvated quercetin molecule and the properties of anhydrous and mono(di)hydrated quercetin crystals employing Density Functional Theory (DFT) calculations with a dispersion correction scheme. Unit cell geometry optimization of the anhydrous crystal has elucidated the structure of the anhydrous quercetin crystal (space group P21/a, monoclinic). Anhydrous quercetin exhibits a direct bandgap of 2.17 ​eV with large valence band dispersion, suggesting a semiconductor behavior for hole transport. Monohydrate quercetin has an indirect gap of 1.84 ​eV, while the solid dihydrate form has a Kohn-Sham indirect electronic bandgap of 2.00 ​eV, smaller than the experimental optical absorption bandgap of 2.40 ​eV. Applying the Δ-sol gap correction scheme, the bandgaps increase by about 1 ​eV. There is a significant optical anisotropy for all quercetin systems in the solid state, especially for the anhydrous form.

A structural investigation of organic battery anode materials by NMR crystallography.

Conjugated alkali metal dicarboxylates have recently received attention for applications as organic anode materials in lithium- and sodium-ion batteries. In order to understand and optimise these materials, it is important to be able to characterise both the long-range and local aspects of the crystal structure, which may change during battery cycling. Furthermore, some materials can display polymorphism or hydration behaviour. NMR crystallography, which combines long-range crystallographic information from diffraction with local information from solid-state NMR via interpretation aided by DFT calculations, is one such approach, but this has not yet been widely applied to conjugated dicarboxylates. In this work, we evaluate the application of NMR crystallography for a set of model lithium and sodium dicarboxylate salts. We investigate the effect of different DFT geometry optimisation strategies and find that the calculated NMR parameters are not systematically affected by the choice of optimisation method, although the inclusion of dispersion correction schemes is important to accurately reproduce the experimental unit cell parameters. We also observe hydration behaviour for two of the sodium salts and provide insight into the structure of an as-yet uncharacterised structure of sodium naphthalenedicarboxylate. This highlights the importance of sample preparation and characterisation for organic sodium-ion battery anode materials in particular.

Adsorption of NO, NO2 and H2O in divalent cation faujasite type zeolites: a density functional theory screening approach.

Emissions of diesel exhaust gas in confined work environments are a major health and safety concern, because of exposition to nitrogen oxides (NOx). Removal of these pollutants from exhaust gas calls for engineering of an optimum sorbent for the selective trapping of NO and NO2 in the presence of water. To this end, periodic density functional theory calculations along with a recent dispersion correction scheme, namely the Tkatchenko-Scheffler scheme coupled with iterative Hirshfeld partitioning TS/HI, were performed to investigate the interactions between NO, NO2, H2O and a series of divalent cation (Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Fe2+, Cu2+, Zn2+, Pd2+, and Pt2+) faujasites. This enabled the identification of the optimum zeolites to selectively capture NOx in the presence of H2O, with respect to two important criteria, such as thermodynamic affinity and regeneration. Our results revealed that Pt2+ and Pd2+ containing faujasites are the best candidates for effective capture of both NO and NO2 molecules, which paves the way towards the use of these sorbents to address this challenging application.

Regulation and control of Schottky barrier in graphene/MoSe&lt;sub&gt;2&lt;/sub&gt; heteojuinction by asymmetric oxygen doping

Although graphene-based heterostructures exhibit excellent intrinsic properties for device scaling, fabricating low Schottky barrier is still a great challenge to the electrical transport behaviors of nanoelectronic devices. Exploring excellent materials for electronic devices are a research hotspot at present. Graphene not only exhibits excellent physical strength and specific surface area, but also presents high carrier mobility and thermal conductivity. Therefore, graphene has been developed in many fields such as energy, catalysis, etc. However, graphene is a special material with zero band gap, and its electrons and holes are easy to compound, which seriously hinders its development in the applications of electronic and optoelectronic devices. Two-dimensional transition metal dichalcogenides (TMDs) have the advantages of controllable band gap properties, which makes them have a good development in logic circuits and photodetectors. As one of TMD&lt;sub&gt;S&lt;/sub&gt;, MoSe&lt;sub&gt;2&lt;/sub&gt; possesses the advantages of narrower band gap, better electron hole separation and stronger oxidation resistance in the environment. Therefore, the design of graphene and MoSe&lt;sub&gt;2&lt;/sub&gt; heterostructures is an ideal choice for a new generation of nanoelectronic devices. Here, we investigate systematically the effects of asymmetric O doping on the electronic properties and Schottky barrier of graphene/MoSe&lt;sub&gt;2(1–&lt;i&gt;x&lt;/i&gt;)&lt;/sub&gt;O&lt;sub&gt;2&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; heterostructure for the first time by first-principles calculations incorporating semiempirical dispersion-correction scheme. The results indicate that graphene and MoSe&lt;sub&gt;2&lt;/sub&gt; monolayer can form a stable van der Waals heterostructure with preserving their own intrinsic properties. In addition, an n-type schottky contact with a barrier height of 0.558 eV is obtained. Further, it is found that the type and the height of the Schottky barrier can be controlled by changing the concentration and sites of the O dopant at interface. By increasing the concentration of the O dopant inside the interface, the transition from an n-type Schottky contact to an Ohmic contact can be realized, and a low n-type Schottky barrier is gained with increasing the concentration of the O dopant outside the interface for highly efficient charge transfer. The barrier height of heterostructure decreases from 0.558 eV to 0.112 eV when the O dopant is doped on the outer interface. Finally, as a complement to previous results, it is confirmed that the redistribution of interfacial charges leads the Fermi level to shift, and thus determining the type and the height of Schottky barrier. This study may provide theoretical guidance for designing and manufacturing the MoSe&lt;sub&gt;2&lt;/sub&gt;-based nano field effect transistors.

Assessing Density Functional Theory for Chemically Relevant Open-Shell Transition Metal Reactions.

Due to the principle lack of systematic improvement possibilities of density functional theory, careful assessment of the performance of density functional approximations (DFAs) on well-designed benchmark sets, for example, for reaction energies and barrier heights, is crucial. While main-group chemistry is well covered by several available sets, benchmark data for transition metal chemistry is sparse. This is especially the case for larger, chemically relevant molecules. Addressing this issue, we recently introduced the MOR41 benchmark which covers chemically relevant reactions of closed-shell complexes. In this work, we extend these efforts to single-reference open-shell systems and introduce the "reactions of open-shell single-reference transition metal complexes" (ROST61) benchmark set. ROST61 includes accurate coupled-cluster reference values for 61 reaction energies with a mean reaction energy of -42.8 kcal mol-1. Complexes with 13-93 atoms covering 20 d-block elements are included, but due to the restriction to single-reference open-shell systems, important elements such as iron or platinum could not be taken into account, or only to a small extent. We assess the performance of 31 DFAs in combination with three London dispersion (LD) correction schemes. Further, DFT-based composite methods, MP2, and a few semiempirical quantum chemical methods are evaluated. Consistent with the results for the MOR41 closed-shell benchmark, we find that the ordering of DFAs according to Jacob's ladder is preserved and that adding an LD correction is crucial, clearly improving almost all tested methods. The recently introduced r2SCAN-3c composite method stands out with a remarkable mean absolute deviation (MAD) of only 2.9 kcal mol-1, which is surpassed only by hybrid DFAs with low amounts of Fock exchange (e.g., 2.3 kcal mol-1 for TPSS0-D4/def2-QZVPP) and double-hybrid (DH) DFAs but at a significantly higher computational cost. The lowest MAD of only 1.6 kcal mol-1 is obtained with the DH DFA PWPB95-D4 in the def2-QZVPP basis set approaching the estimated accuracy of the reference method. Overall, the ROST61 set adds important reference data to a sparsely sampled but practically relevant area of chemistry. At this point, it provides valuable orientation for the application and development of new DFAs and electronic structure methods in general.

Understanding the Crystal Structure of Heterometallic Metal-Organic Frameworks in Cadmium Imidazolate Framework-1 with Periodic Density Functional Theory

Determining the effect of mixed-metal in metal-organic frameworks (MOFs) is vital to understand the crystal structure and its related properties. The tunability of MOFs provides an opportunity to develop functionalized materials with a specific task. Herein, cadmium imidazolate framework-1 (CdIF-1) as part of MOFs was investigated through a computational approach regarding its possibility for the formation of mixed-metal CdIF-1. The studies were performed by replacing Cd2+ ions in the crystal structure of CdIF-1 with Zn2+ ions to obtain several possible configurations of heterometallic CdIF-1. The calculations were conducted using periodic density functional theory (DFT) with the addition of dispersion correction scheme. Several aspects in the crystal structure were investigated such as the changing in the lattice parameters and unit cell volume, and the bond properties. Replacing several Cd2+ ions with Zn2+ would affect the crystal structure particularly lattice parameters and pore diameters. When all the Cd2+ ions were replaced with Zn2+ ions, a new crystal phase was obtained to give zeolitic imidazolate framework-8 (ZIF-8) material. This study provides an insight into the mechanism in which CdIF-1 is transformed into new crystal phase of ZIF-8.

Solid-state nuclear magnetic resonance study of polymorphism in tris(8-hydroxyquinolinate)aluminium.

Tris(8-hydroxyquinolinate)aluminium (Alq3 ) is a metal-organic coordination complex, which is a widely used electroluminescent material in organic light-emitting diode technology. Crystalline Alq3 is known to occur in five polymorphic forms (denoted α, β, γ, δ, and ε), although the structures of some of these polymorphs have been the subject of considerable debate. In particular, the structure of α-Alq3 , which is a model for the local structure in amorphous films used in devices, is highly complex and has never been conclusively solved. In this work, we use solid-state nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations to investigate the local structure of four Alq3 samples. We find that the first structure proposed for α-Alq3 is inconsistent with all of the samples studied, and DFT calculations further suggest that this structure is energetically unfavourable. Instead, samples containing the meridional (mer) isomeric form are found to contain local structures consistent with ε-Alq3 , and a sample containing the facial (fac) isomeric form is consistent with a mixture of γ-Alq3 and δ-Alq3 . We also investigate the influence of different strategies for dispersion correction in DFT geometry optimisations. We find that a recently proposed modified semiempirical dispersion correction scheme gives good agreement with experiment. Furthermore, the DFT calculations also show that distinction between mer and fac isomers on the basis of ηQ that has been assumed in previous work is not always justified.

Computational density-functional approaches on finite-size and guest-lattice effects in CO2@sII clathrate hydrate.

We performed first-principles computations to investigate guest-host/host-host effects on the encapsulation of the CO2 molecule in sII clathrate hydrates from finite-size clusters up to periodic 3D crystal lattice systems. Structural and energetic properties were first computed for the individual and first-neighbors clathrate-like sII cages, where highly accurate ab initio quantum chemical methods are available nowadays, allowing in this way the assessment of the density functional (DFT) theoretical approaches employed. The performance of exchange-correlation functionals together with recently developed dispersion-corrected schemes was evaluated in describing interactions in both short-range and long-range regions of the potential. On this basis, structural relaxations of the CO2-filled and empty sII unit cells yield lattice and compressibility parameters comparable to experimental and previous theoretical values available for sII hydrates. According to these data, the CO2 enclathration in the sII clathrate cages is a stabilizing process, either by considering both guest-host and host-host interactions in the complete unit cell or only the guest-water energies for the individual clathrate-like sII cages. CO2@sII clathrates are predicted to be stable whatever the dispersion correction applied and in the case of single cage occupancy are found to be more stable than the CO2@sI structures. Our results reveal that DFT approaches could provide a good reasonable description of the underlying interactions, enabling the investigation of formation and transformation processes as a function of temperature and pressure.

Insight into the structure of the heulandite-type zeolite containing aromatic compounds using periodic density functional theory

The heulandite-type zeolite (HEU) is an important class of naturally occurring zeolite materials. The recent development of a synthetic HEU zeolite with a high Si/Al ratio opens new possibilities for various applications. Herein, a periodic density functional theory with dispersion correction scheme (DFT-D3) was performed on the HEU-type zeolite. Various aspects of zeolite properties, such as the distribution of Al atoms within the zeolite framework, the prediction of the non-Löwenstein structure, and the presence of aromatic compounds within the cavity, were investigated. Calculation of the initial HEU framework shows that the Al atoms occupy the T2 and T3 sites in the most stable structure. Additionally, a non-Löwenstein structure was predicted for the first time to give a relatively stable HEU structure containing the Al–O–Al configuration. The preferred location of various aromatic compounds, namely, benzene, toluene and naphthalene, could be modeled in the 10-member ring channel to represent a host-guest system in this zeolite with a Si/Al ratio of 10. The results exemplify the importance of understanding the crystal structure of zeolites and the effect it has because of the presence of Al atoms and adsorbate molecules within the zeolite frameworks.

Controlling the spin-crossover behavior of the [Cr(indenyl)2] family via ligand functionalization.

In this work, a computational method to study the spin-crossover (SCO) behavior of the [Cr(n-Meindenyl)2] family was carried out. Using the TPSSh/Def2TZVP method with the GD3BJ dispersion correction scheme, we computed the thermochemistry and transition temperatures (T1/2) for all members of this family, which are in excellent agreement with the available experimental data. Moreover, the computed data allow us to build a model that describes the effect of functionalizing the indenyl ligand in different positions on the spin-state energy gap and transition temperature. Our results show that the C4 and C7 positions of the indenyl ligand have a greater effect on tuning the SCO properties of such complexes. The model quantitatively reproduces the DFT calculations, thus providing a powerful tool to analyze and predict the SCO properties in any member of the [Cr(n-Meindenyl)2] family.

Modified Density Functional Dispersion Correction for Inorganic Layered MFX Compounds (M = Ca, Sr, Ba, Pb and X = Cl, Br, I).

MFX (M = Ca, Ba, Sr, Pb and X = Cl, Br, I) compounds have received considerable attention due to their technological application as X-ray detectors, pressure sensors, and optical data storage materials, when doped with rare-earth ions. MFX compounds belong to the class of layered materials with a tetragonal Matlockite crystal structure, characterized by weakly stacked double-halide layers along the crystallographic c-axis. These layers predominantly determine phase transitions, elastic, and mechanical properties. However, the correct description of the lattice parameter c is a challenge for most standard DFT functionals, which tend to overestimate the lattice parameter c. Because of the weak interactions between the halide layers, dispersion-corrected functionals seem to be a better choice. We investigated 11 different inorganic layered MFX compounds for which experimental data are available, with standard and dispersion-corrected functionals to assess their performance in reproducing the lattice parameter c, structural, and vibrational properties of the MFX compounds. Our results revealed that these functionals do not describe the weak interactions between the halide layers in a balanced way. Therefore, we modified Grimme's popular DFT-D2 dispersion correction scheme in two different ways by (i) replacing the dispersion coefficients and van der Waals radii with those of noble gas atoms or (ii) increasing the van der Waals radii of the MFX atoms up to 40%. Comparison with the available experimental data revealed that the latter approach applied to the PBE (Perdew-Burke-Ernzerhof)-D2 functional with 30% increased van der Waals radii, which we coined PBE-D2* (Srvdw 1.30) is best suited to fine-tune the description of the weak interlayer interactions in MFX compounds, thus significantly improving the description of their structural, vibrational, and mechanical properties. Work is in progress applying this new, computationally inexpensive scheme to other inorganic layered compounds and periodic systems with weakly stacked layers.