HF DFT Research Articles

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.

Experimental and Theoretical Insights into Influence of Hydrogen and Nitrogen Plasma on the Water Splitting Performance of ALD Grown TiO2 Thin Films

Specific effects of hydrogen and nitrogen plasma treatment on anatase TiO2 photoanodes, grown via atomic layer deposition (ALD), and their respective impact on water splitting properties are reported. ALD grown TiO2 samples were exposed to reactive hydrogen and nitrogen plasmas and the photoelectrochemical efficiency of the modified samples were comparatively analyzed. Both H2 and N2 plasma treatment enhanced the photocurrent values compared to pristine TiO2. Electron density at oxygen vacancy sites was decreased upon nitrogen incorporation, reflected in band gap modulation and decreased recombination probability as confirmed by spectral data. Surface modification via H2 plasma induce more midgap states to augment the photoinduced charge carriers concentration that was supported by theoretical investigation performed on the electronic properties of both H- and N-doped TiO2 (anatase). First-principles calculations based on Hartree–Fock–Density Functional Theory (HF–DFT) hybrid models showed good agreement ...

Turn: Weak Interactions and Rotational Barriers in Molecules—Insights from Substituted Butynes

The nature of the bonding and a definite preference for an eclipsed geometry in several substituted but-2-ynes, including certain novel derivatives are uncovered and examined. In particular, we consider the molecular species R3C-C≡C-CR3 (where R= H, F, Cl, Br, I, and CN), their R3C-B≡N-CR3 analogues, and a few novel exo-bridge systems with intramolecular hydrogen bonds running parallel to the C-C≡C-C chain. In some cases, the potential energy surfaces are remarkably flat-so flat, in fact, that free rotation is predicted for those molecules at very low temperatures. A systematic investigation of the bonding in the halogenated butynes demonstrates that the eclipsed conformation actually becomes more stable relative to the staggered form as R becomes larger and less electron-withdrawing. The rotational barriers (the differences in energy between the eclipsed and staggered geometries) are magnified significantly, however, in a special case where selected R groups at the ends of the R3C-C≡C-CR'3 molecule form hydrogen bonds parallel to the C-C≡C-C core. In those systems, the hydrogen bonds serve as a weak locking mechanism that favors the eclipsed conformation. A comparison of HF and uncorrected DFT methods versus the MP2(full), CCSD(T), and other dispersion-corrected methods confirms that correlation accounts to a significant extent for barriers in substituted butyne compounds. In the hydrogen-bonded systems, the barriers are comparable to and larger in some cases than the barriers observed for the more extensively studied ethane molecule.

Method and basis set investigation for trans-platinum(II) oxime complex

The optimized molecular structure and stretching frequencies of platinum(II) oxime complex were investigated with HF, MP2, pure and hybrid DFT methods. CEP-4G, CEP-31G, CEP-121G, LANL2DZ, LANL2MB and SDD basis sets were used in calculations. Correlation coefficients of bond lengths and angles, computational job cpu time and stretching frequencies were used to determine the best method and basis set. The results show that HF/CEP-31G is the best level for bond lengths, angles and computational job cpu time. BPW91/CEP-31G is the best levels for stretching frequencies of oximato-bridged Pt(II) complex.

First Principle Calculations of the Electronic and Vibrational Properties of the 3-(1,1-Dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole Molecule

Results of first principle quantum chemical calculations of electronic and vibrational properties of the push-pull 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) molecule are reported and discussed. The structure of DCNP was optimized with HF/6-311G methodology and found to be planar. On the basis of obtained geometry, infrared absorption and Raman spectra were computed within the HF/6-311++G** formalism. They allow to conclude that the changes of molecule dipole moment and variation of its polarizability appear at the same vibrational mode and affect the optical properties of the DCNP. Four different methodologies: time-dependent HF and time-dependent DFT method with B3LYP, LC-BLYP, and CAM-B3LYP potentials were used to compute the optical absorption spectra of DCNP. Influence of solvent on molecular electronic structure was studied within the C-PCM model. It predicts the DFT/B3LYP methodology as the best one to compute the NLO properties of the DCNP. The computed HOMO and LUMO orbitals show evidence that the ground state of the molecule is located at its aromatic part. The discussion of charge transfer during the excitation process for the transition S0-S1 was performed. The charge transfer parameter calculated in vacuum and in solvent gives the evidence that the solvent environment weakly enhance the molecular charge transfer. It confirms the tendency of an occurrence of the intermolecular charge transfer in DCNP which is crucial for its hyperpolarizability magnitude. It was proved that the second-order susceptibility corresponding to SHG may be calculated for host-guest polymer/DCNP composite using the simple oriented gas model and the rigorous local field approach should not necessarily be applied.

Molecular structure and solvent effects on the dipole moments and polarizabilities of some aniline derivatives

This work presents the quantum chemical studies of the effects of substituents and solvents on the ground state molecular geometry, dipole moments, polarizabilities and frontier orbital energies of aniline (A), N-methylaniline (NMA), N-ethylaniline (NEA), N,N-dimethylaniline (DMA) and N,N-diethylaniline (DEA) towards understanding their structure–property relationship. The ground state molecular geometry, dipole moments, polarizabilities and frontier orbital energies of A, NMA, NEA, DMA and DEA were computed by use of the ab initio restricted HF–DFT self-consistent field method (B3LYP) with 6-31G* basis set in vacuum, ethanol and tetrahydrofuran. The results of the B3LYP/6-31G* calculations revealed that these properties are enhanced upon successive substitution with size and number of alkyl groups at the amino group of the molecules, and as the dielectric constant of the solvents decrease. It was also found that for all the molecules, the enhanced ground state molecular geometry, dipole moments and polarizabilities upon substitution or solvent effect are associated with a decrease in the EHOMO−ELUMO (optical) gap. The lower optical gap, higher dipole moments and polarizabilities with increased size and planarity illustrates increased reactivity and ground state electro-optic (non-linear optical) activity of the molecules upon substitution, and as the dielectric constant of the solvents decreased. Of the studied molecules, DEA was found to exhibit the most electro-optic activity and reactivity.

Ab initio and DFT study of the dipole (hyper) polarizabilities of p-nitrophenylphosphine molecule

The static dipole hyper polarizabilities α,β and γ of p-nitrophenylphospine PNPhP, a hypothetical Push-Pull organic molecule, were calculated using ab initio HF, MP2, MP4 and density functional theory DFT B3LYP, CAM-B3LYP, WB97X-D hybrid approaches, in conjunction with the standard 6-31+Gd,p and 6-311++G3d,3p basis sets. Similar hyper polarizability calculations were additionally carried out for p-Nitroaniline PNA molecule for comparison purposes. These response properties were evaluated within the Finite Field methodology based in the Kurtz equations, where the effects of replacing the -NH_{2} donor group of PNA by the -PH_{2} group originating the p-nitrophenylphospine PNPhP molecule are analyzed. The results of α, β and γ properties evaluated at different levels of theory show that PNPhP molecule is much more hyperpolarizable than PNA one. Electron correlation effects, evaluated at MP2, MP4, DFT/B3LYP, CAM-B3LYP and WB97X-D levels of theory, show that α_{ave} increases between 7 to 16% with respect to the HF values. Likewise, the largest responses are obtained with the most extended basis sets such as 6-311++G3d,3p, where polarizability increase between 4 to 9% with respect to 6-31+Gd,p one. The tendencies for β and γ NLO values follow the electron density delocalization of the molecular system, that is more extended in PNPhP than PNA one. Electron correlation effects increase β and γ properties in the order of two or three times with respect to the HF values. Finally, the impact of dynamic and solvent effects on the first hyperpolarizability of PNA molecule were also taken into account, which are discussed in terms of recent literature. The analysis of results, allow us to conclude that PNPhP is an interesting hypothetic molecule that can be useful as building block for the design and creation of new materials with enhanced nonlinear optic applications.

Increasing the applicability of DFT I: Non-variational correlation corrections from Hartree–Fock DFT for predicting transition states

Hartree–Fock DFT (HF-DFT) uses the self-interaction error free HF density and DFT functional. Using HF-DFT for molecular structure determination requires a non-variational analytical gradient scheme. This has been developed and applied for the calculation of transition state geometries and barrier heights for chemical reactions. The barrier heights obtained show average absolute errors (AAE) of 2–3kcal/mol while ΛCCSD(T) show an AAE of 1.1–1.4kcal/mol. Standard variational DFT with the same functional has AAE’s of 6.3–8.3kcal/mol while the HF errors are about 12kcal/mol.

Sensorless Control of IPM Motors in the Low-Speed Range and at Standstill by HF Injection and DFT Processing

In this paper, a sensorless controller for an interior permanent-magnet synchronous motor is presented based on well-known high-frequency signal injection techniques. The issue of the demodulation process is the key point of this paper. A novel approach based on discrete Fourier transform and nonconventional reference frame transformation is presented, allowing a simple and robust noncoherent demodulation, i.e., in which no information about the carrier phase is needed. In the classically adopted coherent approaches, in fact, uncertainty about carrier phase reflects in uncertainty in the demodulated signal amplitude, affecting observer gains and signal-to-noise ratio and definitively providing a degradation of the performance of the estimator. Analytical development of the sensorless algorithm, including the demodulation technique, is provided. A complete investigation by simulation is carried out aiming at showing the performance of the proposed method. Finally, experimental results are presented based on a prototype motor drive for city scooters.

Structure and Conformational Stability of Protonated Dialanine

A systematic investigation on the structure and stability of the four conformers of the protonated dialanine cation (transA1, transA2, transO1, cisA3) was performed employing the HF, MP2, and hybrid DFT methods with various basis sets which ranged from the 6-31G* to the basis set larger than the correlation consistent aug-cc-pVTZ basis set. It is found that the backbone dihedral angles and energies of the conformers are sensitive to the electron correlation level and basis set, especially manifesting slow convergence of conformer structure and energetics with basis set at the MP2 level. At the MP2 basis set limit corrected by CCSD(T) correlation effect, the lowest transA1 conformer is almost isoenergetic with the cisA3 conformer, followed by the transA2 conformer ( approximately 0.5 kcal/mol above transA1), and, last, the transO1 conformer ( approximately 1.2 kcal/mol above transA1). Vibrational and thermal (entropic) factors appear to have an important effect on the relative stability between conformers at room temperature, reducing the energy difference between transA1 and transA2 conformers and making cisA3 higher in energy than transA1 or transA2, which is in accord with the recent infrared multiphoton dissociation experimental data on this cation. According to the polarizable continuum model calculations, solvation of protonated dialanine in water would significantly enhance the stability of the transA2 conformer, making it most populated in aqueous solution at room temperature. Among the tested hybrid DFT methods in this study, B3LYP/6-31G* was found to be the most effective for predicting the conformational structures and relevant stability of protonated dialanine cation in the gas phase.

Hybrid HF–DFT modeling of monolayer water adsorption on (001) surface of cubic BaHfO 3 and BaZrO 3 crystals

First-principles calculations have been used to study the atomic structure, preferred sites and adsorption energies for water adsorption at different terminations of the cubic phase of perovskite-structured BaHfO 3 and BaZrO 3. By considering different initial positions of water molecules, the possibility of water dissociation has been investigated. It is demonstrated that the site selectivity and the form of adsorbed molecule can be affected by the choice of surface unit cell. Dissociative adsorption was found to be favorable for all surfaces in consideration. Hydroxylation of ZrO 2- and HfO 2-terminated surfaces is accomplished by a noticeable reconstruction of the surface structure of cubic phase towards the orthorhombic phase. Calculated atomic charges in bare and hydroxylated surfaces show that BaHfO 3 crystal is slightly more ionic than BaZrO 3.

Synthesis, X-Ray characterization and molecular structure of a novel supramolecular compound of antimony(III); Theoretical investigation on molecular and electronic properties based on the ab initio HF and various DFT methods

A new compound of Sb(III), formulated as (pipzH2)[Sb2(pydc)4].2H2O (1), was synthesized and characterized by IR, 1H and 13C NMR spectroscopy, elemental analysis and single crystal X-ray diffractometry. The compound (1) is a member of a great family of supramolecular metallic compounds recently derived from a proton transfer ion pair i.e. (pipzH2)(pydc), where pipz is piperazine and pydcH2 is pyridine-2,6-dicarboxylic acid. In the title compound with a binuclear structure, Sb(III) atoms are pentacoordinated and the coordination polyhedra show distortion from a regular trigonal bipyramid due to stereochemically active lone pair on metallic centers. The four (pydc)2− ligands of the formula unit behave differently against metallic centers, i.e. two act as tridentate, and the other two as bidentate ligands. A variety of intermolecular O-H…O, N-H…O and C-H⋯O hydrogen bonds involving water molecules, cationic and anionic fragments are responsible for the extension of the supramolecular network of the compound. Optimized geometries were calculated for the title compound with the HF, B3LYP, B3PW91, B3P86 and B1LYP methods of theory by using the combination of LanL2DZ basis set with standard basis set 6-31G (d,p). The agreement between the optimized and experimental geometries was in the decreasing order: B3P86, B3PW91, B1LYP, B3LYP and HF. Electronic properties of the title compound were also investigated based on the natural bond orbital (NBO) analysis.

Geometric Isotope Effect on Low Barrier Hydrogen-Bonding Systems of Acetic Acid Dimer, Formic Acid Dimer, and Their Anionic Clusters by Using the Multi-Component Molecular Orbital Method

The geometric isotope effect (GIE) on low barrier hydrogen-bonded systems of acetic acid dimer, formic acid dimer, and their anion clusters is analyzed by HF and hybrid DFT levels of the multi-component molecular orbital (MC_MO) method, which directly includes nuclear quantum effect of proton/deuteron. Our optimized geometries for both neutral and anionic species with HF level of MC_MO method have reproduced the overall tendency of the GIE of the corresponding experimental ones. On the other hand, the results for anionic clusters with hybrid BHandHLYP functional of MC_MO method give poor agreement due to the underestimation of the barrier height of hydrogen-bonding. Our multi-component analysis clearly demonstrates that the hydrogen-bonding interaction energy is strongly affected by the distribution of nuclear wavefunction.

Structural and electronic properties of gold microclusters: assessment of the localized Hartree–Fock method

We assess the localized Hartree-Fock (LHF) method for the simulation of the structural and electronic properties of gold microclusters. We compute the minimum-energy geometries, atomization energies, dipole moments, and single-particle spectra for five gold clusters, Au(N), and their anions, Au(N)-, with N < or = 4. Calculations are performed with the LHF functional, with and without the addition of the Lee-Yang-Parr (LYP) correlation, and the results are compared with those obtained from other semilocal and hybrid functionals as well as from Hartree-Fock calculations. The LHF functional yields structural properties of similar quality to the other exchange-only methods, but superior molecular orbital energies are found. The LHF single-particle spectrum is free of the artifacts typical for HF and standard DFT calculations and in good agreement with available experimental reference data. The inclusion of correlation by the LYP functional produces a significant improvement of geometries and energetics, but has only a minor impact on the orbital energies.

Fuzzy fragment selection strategies, basis set dependence and HF–DFT comparisons in the applications of the ADMA method of macromolecular quantum chemistry

AbstractThe Adjustable Density Matrix Assembler (ADMA) method is examined in this paper. This method approximates (first order) density matrices by taking only those interactions into account which are present between fragments separated by a preset distance parameter (d). The accuracy of this approximation is tested using different basis sets, distance parameters and exchange‐correlation functionals. As an illustration of the applications of the method, the electron density of the hemoglobin molecule is presented in its oxy, deoxy and carbon‐monoxy form. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Theoretical prediction of gas-phase infrared spectra of imidazo[1,2- a]pyrazinediones and imidazo[1,2- a]imidazo[1,2- d]pyrazinediones derived from glycine

Imidazo[1,2- a]pyrazine-3,6-diones and imidazo[1,2- a]imidazo[1,2- d]pyrazine-3,8-diones can be produced by pyrolysis of simple amino acids. While such bicyclic and tricyclic amidines were detected and characterized by IR spectroscopy for some α-substituted amino acids, the parent systems composed of glycine fragments are unknown up to now. IR spectra for five amidines derived from glycine were calculated by using different semi-empirical (PM3, AM1, MNDO and MINDO/3), HF, and hybrid DFT (B3LYP, B3P86 and B3PW91) methods in conjunction with 6-31G( d) basis set (for HF and DFT). Vibration frequencies in the experimental IR spectra were predicted based upon the B3LYP data, by correcting the calculated wavenumbers by a scaling factor of 0.959. The behavior of most characteristic bands ( ν C X , ν NH, etc.) and their shifts with respect to such bands in the spectra of alanine and α-aminoisobutyric acid derivatives studied before, are discussed. Performance of the semi-empirical methods was tested, bearing in mind possible future needs for IR spectra predictions for larger molecular systems of similar chemical nature; the use of MINDO/3 and MNDO is recommended. A basis set effect on the B3LYP fundamental vibration frequencies for hexahydroimidazo[1,2- a]pyrazine-3,6-dione was studied by varying Pople basis sets from minimal STO-3G to 6-311++G( d, p). No significant improvements were found beyond the 6-31G( d) basis set, which thus can be recommended to predict IR spectra for the amidines and similar molecules.

Coordinated and clathrated guests in the 3infinity[Hg6As4]4+ bicompartmental framework: synthesis, crystal and electronic structure, and properties of the novel supramolecular complexes [Hg6As4](CrBr6)Br and [Hg6As4](FeBr6)Hg0.6.

Two new supramolecular complexes [Hg(6)As(4)](CrBr(6))Br (1) and [Hg(6)As(4)](FeBr(6))Hg(0.6) (2) have been prepared by the standard ampoule technique and their crystal structures determined. Both crystallize in the cubic space group Pa$\bar 3$ with the unit cell parameter a=12.275(1) (1) and 12.332(1) A (2), and Z=4. Their structures consist of bicompartmental, three-dimensional [Hg(6)As(4)](4+) frameworks with cavities of two different sizes occupied by guest anions of different type. The bigger cavities are filled with the octahedral MBr(6) (n-) ions (M=Cr or Fe; n=3 or 4), whereas the smaller cavities trap either Br- ions (1) or Hg(0) (2). The analysis of the host-guest contacts has allowed a classification of the octahedral guests as coordinated and the monatomic guests as clathrated. Magnetic measurements and ESR spectroscopy data have given information about the interaction between the host and guests. Band structure calculations (HF and hybrid DFT level) indicate that both 1 and 2 are non-metallic, with a band gap of approximately 1.5 eV (B3LYP), and that the interaction between the host and guests is of predominantly electrostatic character. It is shown that though the electrostatic host-guest interaction is weak it plays an important role in assembling the perfectly ordered supramolecular architectures.

On the correlation between kinetic rate constants in the auto-ignition process of some oxygenates and their cetane number: a quantum chemical study

This theoretical study investigates the chemical reactivity of several oxygenates with molecular oxygen in the context of the use of oxygenates as Diesel fuel additives. The general objective consists in testing the hypothesis according to which the cetane number (CN) of a pure compound fuel depends essentially on the rate of initiation of the homogeneous gas phase reaction of this compound with oxygen. To this end theoretical calculations of rate constants for this initiation step were conducted for a series of organic compounds. These molecules were selected to be small enough that these calculations are feasible and because reliable measurements of their CNs were available. Ab initio molecular orbital calculations are carried out with both Hartree–Fock and density functional theory (HF–DFT) methods in conjunction with the 6-311G(p,d) basis set. Structural, energetic, vibrational spectra, thermodynamic and kinetic parameters of the auto-ignition process are evaluated for the gas-phase initiation reactions R–H+O 2→R +O 2H , where RH is dimethyl ether, diethylether, methanol, methylal or propane (propane is taken as a reference). The initiation step reaction rate constants at the temperatures 298.15 and 1000 K are calculated using the kinetic model based on the conventional transition state theory (TST) method. In both levels of theory used, a fair correlation is observed between calculated rate constants of the hydrogen atom abstraction process and experimental values of the CN of these pure compounds. Nonetheless, a better correlation is obtained using the HF–DFT method for rate constant calculations at high temperature which is relevant to operating conditions of Diesel engines. The correlation obtained in this work yields a first confirmation of the hypothesis according to which only the rate of the initiation step in the auto-ignition sequences of reactions determines the value of the CN of the pure compounds.

Vibronic spectroscopy of the H-bonded aminophenol–water complex

In this work, the vibronic spectroscopy of the p-aminophenol–water 1:1 complex is presented. The S1 vibrational energy levels of the complex were characterized by REMPI spectroscopy up to 2500 cm−1 above the band origin. The dispersed fluorescence spectra were recorded for the B.O., 6a01 and I02 excitations to characterize the vibrational levels in the S0 state of the complex. Stimulated ion depletion spectroscopy was carried out to determine the higher vibrational levels of the ground state all the way up to ∼3075 cm−1. The structure and the vibrational levels of the AP–W1 complex were calculated ab initio at the HF level and DFT with B3LYP functional for S0, and CIS level for S1 using 6-31G** basis set. The structure of the AP–W1 complex compared well with the earlier calculations for this case as well as the other ROH–water (R=aromatic group) complexes reported in the literature. However, the redshift in the electronic band origin was almost half of that observed in other cases. A good correlation was shown to exist between the electronic red shifts and the respective pKa* values (the pKa in the excited state).

Conformational Preferences of the Base Substituent in Hypermodified Nucleotide Queuosine 5′-monophosphate ‘pQ’ and Protonated Variant ‘pQH+’

Conformational preferences of the base substituent in hypermodified nucleotide queuosine 5′-monophosphate ‘pQ’ and its protonated form ‘pQH+’ have been studied using quantum chemical Perturbative Configuration Interaction with Localized Orbitals PCILO method. The salient points have also been examined using molecular mechanics force field MMFF, parameterized modified neglect of differential overlap PM3 and Hartree Fock-Density Functional Theory HF DFT (pBP/DN*) approaches. Aqueous solvation of pQ and pQH+ has also been studied using molecular dynamics simulations. Consistent with the observed crystal structure, in isolated protonated form pQH+, the quaternary amine HN(13)+H, of the sidechain having 7-aminomethyl linkage, hydrogen bonds with the carbonyl oxygen O(10) of the base. However, N(13)H—0(10) hydrogen bonding is not preferred for unprotonated pQ, whether isolated or hydrated. Interaction between the 5′-phosphate and the 7-aminomethyl group is more likely for isolated pQ. The cyclopentenediol hydroxyl group 04″H may hydrogen bond with the 0(10) in isolated pQ as well as in pQH+. The 04″H may hydrogen bond with the 5′-phosphate as well. The presence of -CH2-NH- and 0″H groups in pQ and pQH+ allows interesting possibilities for intranucleotide hydrogen bonds and interactions across the anticodon loop. Simultaneous hydrogen bonds 02P—HN(13)+H—0(10) are indicated for hydrated pQH+. Unlike weak involvement of 04″H, these interactions also persist in hydrated pQH+ and may much reduce backbone flexibility. Resulting sub-optimal Q:C base pairing leads to unbiased reading of U or C as the third codon letter. Cyclopentenediol hydroxyl groups may interact with other biomolecules, allowing specific recognition. Prospective pQ34 and pQ34H+ sites for codon-anticodon base pairing remain unhindered, but non canonical Q:G base pairing (amber-suppression) is ruled out.