Potential Energy Curves Research Articles

Investigation of Ga–Nb co-doped barium strontium titanate ceramics for DC-bias free dielectrics

The Ba0.8Sr0.2Ti1−2x Ga x Nb x O3 (0 ≤ x ≤ 0.10) ceramics were fabricated and the electrical properties were evaluated regarding DC-bias and temperature characteristics of the dielectric properties. The ceramics with x = 0.10 exhibited a stable dielectric constant with a change of–40% within 25 °C–150 °C. The dielectric loss of all the co-doped ceramics was below 2% within 25 °C–200 °C. The Ba0.8Sr0.2Ti1−2x Ga x Nb x O3 ceramics showed a higher dielectric constant with a lower DC-bias dependence as compared to previous study on co-doped BaTiO3 ceramics. The Ba0.8Sr0.2Ti0.20Ga0.10Nb0.10O3 ceramics exhibited the best results of DC-bias dependence ≈−24%, dielectric constant at 100 kV cm−1 ≈ 560, and the dielectric constant at 0 kV cm−1 ≈ 735. The better results for the Ga–Nb co-doped BST ceramics might be due to the higher contribution of the ionic polarization in the BST base matrix resulting in a shallower potential energy curve.

Enhancing the antioxidant potential of ESIPT-based naringenin flavonoids based on excited state hydrogen bond dynamics: A theoretical study

Exploring antioxidant potential of flavonoid derivatives after ESIPT process provides a theoretical basis for discovering compounds with higher antioxidant capacity. In this work, employing the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods, the antioxidant potential of two citrus-derived naringenin flavonoids after ESIPT process is explored. Based on studies of ESIPT process including IMHB intensity variations, potential energy curves, and transition state, these molecules exist only in enol and keto⁎ forms due to ultra-fast ESIPT. The HOMOs are utilized to explore electron-donating capacity, demonstrating that the molecules in keto⁎ form is stronger than that in enol form. Furthermore, the atomic dipole moment corrected Hirshfeld population (ADCH) and Fukui functions indicate that the sites attacked by the electrophilic free radical of the two molecules in the keto⁎ form are O3 and O5’ respectively, and both are more active than in the enol form. Overall, a comprehensive consideration of the ESIPT process and antioxidant potential of flavonoid derivatives will facilitate the exploration and design of substances with higher antioxidant capacity.

Very Strong Hydrogen Bond in Nitrophthalic Cocrystals.

This work presents the studies of a very strong hydrogen bond (VSHB) in biologically active phthalic acids. Research on VSHB comes topical due to its participation in many biological processes. The studies cover the modelling of intermolecular interactions and phthalic acids with 2,4,6-collidine and N,N-dimethyl-4-pyridinamine complexes with aim to obtain a VSHB. The four synthesized complexes were studied by experimental X-ray, IR, and Raman methods, as well as theoretical Car-Parrinello Molecular Dynamics (CP-MD) and Density Functional Theory (DFT) simulations. By variation of the steric repulsion and basicity of the complex' components, a very short intramolecular hydrogen bond was achieved. The potential energy curves calculated by the DFT method were characterized by a low barrier (0.7 and 0.9 kcal/mol) on proton transfer in the OHN intermolecular hydrogen bond for 3-nitrophthalic acid with either 2,4,6-collidine or N,N-dimethyl-4-pyridinamine cocrystals. Moreover, the CP-MD simulations exposed very strong bridging proton dynamics in the intermolecular hydrogen bonds. The accomplished crystallographic and spectroscopic studies indicate that the OHO intramolecular hydrogen bond in 4-nitrophthalic cocrystals is VSHB. The influence of a strong steric effect on the geometry of the studied cocrystals and the stretching vibration bands of the carboxyl and carboxylate groups was elaborated.

How Well Can Quantum Embedding Method Predict the Reaction Profiles for Hydrogenation of Small Li Clusters?

Quantum computing leverages the principles of quantum mechanics in novel ways to tackle complex chemistry problems that cannot be accurately addressed using traditional quantum chemistry methods. However, the high computational cost and available number of physical qubits with high fidelity limit its application to small chemical systems. This work employed a quantum-classical framework which features a quantum active space-embedding approach to perform simulations of chemical reactions that require up to 14 qubits. This framework was applied to prototypical example metal hydrogenation reactions: the coupling between hydrogen and Li2, Li3, and Li4 clusters. Particular attention was paid to the computation of barriers and reaction energies. The predicted reaction profiles compare well with advanced classical quantum chemistry methods, demonstrating the potential of the quantum embedding algorithm to map out reaction profiles of realistic gas-phase chemical reactions to ascertain qualitative energetic trends. Additionally, the predicted potential energy curves provide a benchmark to compare against both current and future quantum embedding approaches.

Potential energy curves for F2, Cl2, and Br2 with the i-DMFT method.

The potential energy curves for dihalogens (F2, Cl2, and Br2) are calculated with the i-DMFT method proposed recently [Wang and Baerends, Phys. Rev. Lett. 128, 013001]. All electrons are correlated in a set of self-consistent-field eigenvalue equations, with the orbital occupation numbers obeying the Fermi-Dirac distribution. The only input is the dissociation energies of the molecules, which are usually available from an experimental database. The quality of the computed potential energy curve is examined by extracting spectroscopic parameters and rotation-vibration energy levels, which are compared with experiment data and other theoretical calculations.

Theoretical investigation of the electronic structure of the Rhodium Halides molecules RhF and RhCl with dipole moment calculation

The current study involves an ab initio exploration of the ground and low-lying excited electronic states of the rhodium halide molecules RhF and RhCl using the complete active space self-consistent field (CASSCF) with multireference configuration interaction (MRCI+Q) method including single and double excitations and with Davidson corrections. We investigated the potential energy curves, the transition and permanent electric dipole moments, the electronic energy relative to the ground state Te, the harmonic frequency ωe, the internuclear distance Re, and the rotational constant Be corresponding to each of the bounded states. Our findings demonstrate good agreement with the available experimental data. Notably, this work represents the inaugural theoretical investigation of the excited states of RhF and RhCl molecules, identifying the ground state of both to be X3Π, as observed in the sole two experimental investigations.

Theoretical Study of Ground-State Barium-Rare Gas Van der Waals Complexes: Combining Rule Modeling and Ab Initio Calculations.

The present study aims to generate the potential energy curves (PECs) and spectroscopic constants for barium alkaline earth (AE) atoms interacting with rare gas (RG) atoms (He, Ne, Ar, Kr, and Xe). The study focuses on investigating the van der Waals bonds that characterize the interactions between alkaline-earth metals and RG atoms, with a specific emphasis on employing the Tang and Toennies (TT) potential model, known to accurately describe such interactions. The TT potential model was employed in conjunction with combining rules to calculate its parameters, which include dispersion coefficients C 2n and Born-Mayer constants A and b. Additionally, we have conducted high-level ab initio calculations at the CCSD(T) level for all Ba-RG ground states. Obtained PECs from both methods have been used to evaluate the spectroscopic properties D e, R e, ωe, B e, and ωeχe. Our findings reveal that the derived spectroscopic constants from the TT model exhibit good agreement with the results obtained from CCSD(T) calculations and with other available theoretical studies. Furthermore, to gain insights into the relative differences among AE-RG species, we calculated the κ parameter for AE-RG and AE+-RG (AE = Sr, Ca, Mg, Ba; RG = He-Xe) complexes. It is found that except for the case of Ba-RG and Ba+-RG, the κ values within the same series, AE-RG and AE+-RG, are remarkably close to each other.

Tribological behavior of graphene/h-BN vdW heterostructures: the role of defects at the BN layer

Molecular dynamics simulations and first principles calculations were performed to study the tribological behavior of graphene/h-BN (G/h-BN) heterostructures with vacancy and Stone–Wales (SW) defect under uniform normal load, revealing the mechanism of the effect of defect types on friction, and discussing the coupling effect of temperature and interfacial defects on the tribological behavior of G/h-BN heterostructures. Under the normal force of 0.2 nN/atom, the friction force of the four systems is 0.0057, 0.0096, 0.0077, and 0.26 nN, respectively. The friction force of SW defect heterostructure is 45 times that of perfect interface heterostructure. The influence of defect type on friction force is SW > SV > DV. By observing the dynamic change of the Z-direction coordinate position of the sliding layer atoms, the slip potential energy curves and the evolution law of the moiré pattern, the relationship between the structural morphology and the energy change of different defective heterostructures and the frictional behavior was investigated comprehensively and intuitively for the first time. From the perspective of atomic strain, the deformation of heterostructures at the atomic level was quantified. The results showed that at 300 K and 0 K, the maximum strain of atoms in the sliding layer was 11.25% and 9.85%, respectively. The thermal perturbation mainly occurs in the out-of-plane direction, which in turn affects the friction. Through density functional theory, it is found that under uniform load, it is difficult to form bonds between the graphene sliding layer and the substrate layer when the defects are in the h-BN substrate layer, which has less influence on the friction of the system, thus making the defective heterostructures also remainsuperlubricity state. These results provide a new understanding of the interfacial friction of G/h-BN defective heterostructure.

Proton-Coupled Electron Transfer upon Oxidation of Tyrosine in a De Novo Protein: Analysis of Proton Acceptor Candidates.

Redox-active residues, such as tyrosine and tryptophan, play important roles in a wide range of biological processes. The α3Y de novo protein, which is composed of three α helices and a tyrosine residue Y32, provides a platform for investigating the redox properties of tyrosine in a well-defined protein environment. Herein, the proton-coupled electron transfer (PCET) reaction that occurs upon oxidation of tyrosine in this model protein by a ruthenium photosensitizer is studied by using a vibronically nonadiabatic PCET theory that includes hydrogen tunneling and excited vibronic states. The input quantities to the analytical nonadiabatic rate constant expression, such as the diabatic proton potential energy curves and associated proton vibrational wave functions, reorganization energy, and proton donor-acceptor distribution functions, are obtained from density functional theory calculations on model systems and molecular dynamics simulations of the solvated α3Y protein. Two possible proton acceptors, namely, water or a glutamate residue in the protein scaffold, are explored. The PCET rate constant is greater when glutamate is the proton acceptor, mainly due to the more favorable driving force and shorter equilibrium proton donor-acceptor distance, although contributions from excited vibronic states mitigate these effects. Nevertheless, water could be the dominant proton acceptor if its equilibrium constant associated with hydrogen bond formation is significantly greater than that for glutamate. Although these calculations do not definitively identify the proton acceptor for this PCET reaction, they elucidate the conditions under which each proton acceptor can be favored. These insights have implications for tyrosine-based PCET in a wide variety of biochemical processes.

Theoretical Modeling of Sr(q+) He (q = 0, 1, 2) van der Waals Systems Including Spin-Orbit Coupling.

Using an ab initio methodology that incorporates pseudopotential technique in conjunction with pair potential approaches, core polarization potentials (CPP), large basis sets of Gaussian type, and full configuration interaction calculations, we investigate interaction of neutral and charged Srq+(q = 0,1,2) with helium atom. In this context, the core-core interaction of Sr2+-He is included using an accurately performed potential for the ground state at CCSD(T) level of calculation. Also, the potential energy curves and permanent and transition dipole moments of the ground state and numerous excited states have been performed respectively for Sr+He and SrHe systems. Subsequently, the spin-orbit effect is considered by utilizing a semiempirical method for states dissociating into Sr+(5p) + He, Sr+(6p) + He, Sr+(4d) + He, Sr+(5d) + He, Sr(5s5p) + He, and Sr(5s4d) + He. The spectroscopic constants of the Srq+(q = 0, 1, 2) He states, with and without spin-orbit interaction, are derived and assessed in comparison to the existing theoretical and experimental studies. Such comparison has revealed good agreement, especially, for the Sr+He ionic system. Additionally, the spin-orbit effect is considered for the X2Σ+ → 22Π1/2,3/2 and X2Σ+ → 32Σ1/2 + transition dipole moments for Sr+He.

Strategies to Obtain Reliable Energy Landscapes from Embedded Multireference Correlated Wavefunction Methods for Surface Reactions.

Embedded correlated wavefunction (ECW) theory is a powerful tool for studying ground- and excited-state reaction mechanisms and associated energetics in heterogeneous catalysis. Several factors are important to obtaining reliable ECW energies, critically the construction of consistent active spaces (ASs) along reaction pathways when using a multireference correlated wavefunction (CW) method that relies on a subset of orbital spaces in the configuration interaction expansion to account for static electron correlation, e.g., complete AS self-consistent field theory, in addition to the adequate partitioning of the system into a cluster and environment, as well as the choice of a suitable basis set and number of states included in excited-state simulations. Here, we conducted a series of systematic studies to develop best-practice guidelines for ground- and excited-state ECW theory simulations, utilizing the decomposition of NH3 on Pd(111) as an example. We determine that ECW theory results are relatively insensitive to cluster size, the aug-cc-pVDZ basis set provides an adequate compromise between computational complexity and accuracy, and that a fixed-clean-surface approximation holds well for the derivation of the embedding potential. Additionally, we demonstrate that a merging approach, which involves generating ASs from the molecular fragments at each configuration, is preferable to a creeping approach, which utilizes ASs from adjacent structures as an initial guess, for the generation of consistent potential energy curves involving open-d-shell metal surfaces, and, finally, we show that it is essential to include bands of excited states in their entirety when simulating excited-state reaction pathways.

Electronic structure and spectroscopic properties of some low-lying electronic states of neutral and ionic species CN and CN−

ABSTRACT The present work provides Potential Energy Curves (PECs) of both cyano radical CN and cyanide anion CN − up to the third asymptote of dissociation out of ab initio calculations. The [MRCI+Q] method is the level of theory used here and we have associated it with the Dunning basis set AV6Z (Augmented correlation-consistent polarised Valence sextet Zeta) for geometry optimisation of our systems. Electronic configurations of the states of the two species were explored and based on these configurations and the relative positions of the PECs of CN − against those of the neutral radical CN, stable and metastable states have been found and exhibited. The calculated electron affinity here that proves itself to be positive and the position of the X 1 Σ + state against its corresponding neutral parent state ( X 2 Σ + ) from which it derives led to confirm that this state is a long-lived and stable ground state of the cyanide anion CN − . Spectroscopic constants of both ground and low-lying excited states are calculated and exhibited in this work.

Complex potential energy surfaces with projected CAP technique: Vibrational excitation of N2.

The projected complex absorbing potential (CAP) technique is one of the methods that allow one to extend the bound state methods for computing resonances' energies and widths. Here, we explore the accuracy of the potential energy curves generated with different electronic structure theory methods in combination with the projected CAP technique by considering resonant vibrational excitation (RVE) of N2 by electron impact as a model process. We report RVE cross sections computed using the boomerang model with potential energy curves obtained with CAP-based extended multistate complete active space perturbation theory (XMS-CASPT2) and equation of motion coupled-cluster method for electron attachment with single and double substitution (EOM-EA-CCSD) methods. We also compare potential energy curves computed with several electronic structure methods, including XMS-CASPT2, EOM-EA-CCSD, multireference configuration interaction with singles (MR-CIS) and singles and doubles (MR-CISD). A good agreement is observed between the experiment and simulated RVE cross sections obtained with the potential energy curves generated with XMS-CASPT2 and EOM-EA-CCSD methods, thus highlighting the potential of the projected CAP technique combined with accurate electronic structure methods for dynamical simulations of the processes that proceed through metastable electronic states.

Investigating quantum coherence of N-methylpyrrole through vibrational spectroscopy and potential energy: A theoretical study

Quantum chemical calculations are utilized to analyze the potential causes of N-methylpyrrole oscillations, focusing on vibration spectra and potential energy curves. Optimization of the ground state, ionic state and 3s state structure reveal mostly sp2 hybridization. An analysis of the 3s state vibration spectrum and adiabatic binding energy indicate that changes in dihedral angles D2,3,4,1 and plane angle A3,2,1 are potential factors contributing to molecular oscillations. The role of vertical binding energy and adiabatic binding energy in the oscillation process are also discussed, shedding light on the possible dynamic processes of N-methylpyrrole.

Ab initio exploration of low-lying electronic states of linear and bent MNX+ (M = Ca, Sr, Ba, Ra; X = O, S, Se, Te, Po) and their origins.

High-level multireference and coupled cluster quantum calculations were employed to analyze low-lying electronic states of linear-MNX+ and side-bonded-M[NX]+ (M = Ca, Sr, Ba, Ra; X = O, S, Se, Te, Po) species. Their full potential energy curves (PECs), dissociation energies (Des), geometric parameters, excitation energies (Tes), and harmonic vibrational frequencies (ωes) are reported. The first three chemically bound electronic states of MNX+ and M[NX]+ are 3∑-, 1Δ, 1∑+ and 3A″, 1A', 1A″, respectively. The 3∑-, 1Δ, 1∑+ of MNX+ originate from the M+(2D) + NX(2Π) fragments, whereas the 3A″, 1A', 1A″ states of M[NX]+ dissociate to M+(2S) + NX(2Π) as a result of avoided crossings. The MNX+ and M[NX]+ are real minima on the potential energy surface and their interconversions are possible. The M2+NX-/M2+[NX]- ionic structure is an accurate representation for their low-lying electronic states. The Des of MNX+ species were found to depend on the dipole moment (μ) of the corresponding NX ligands and a linear relationship between these two parameters was observed.

A Tale of Two Tails: Rotational Spectroscopy of N-Ethyl Maleimide and N-Ethyl Succinimide.

Broadband microwave spectra of N-ethyl maleimide (NEM) and N-ethyl succinimide (NES) have been recorded using chirped pulse Fourier transform microwave spectroscopy in the Ka-band (26.5-40 GHz). The spectra for both molecules were fit to a Watson A-reduced Hamiltonian in the Ir representation to obtain best fit experimental rotational constants (NEM: A0 = 2143.1988(29), B0 = 1868.7333(22), C0 = 1082.98458(36); NES: A0 = 2061.47756(14), B0 = 1791.73517(12), C0 = 1050.31263(11)), centrifugal distortion constants, and nuclear quadrupole coupling constants. While the heavy atoms of the five-membered ring of both molecules are planar, the ethyl chain has its terminal methyl group perpendicular to the ring. Along the relaxed potential energy curve for the ethyl dihedral angle (θ1 = C(6)-C(5)-N-C(4)), the ethyl group experiences significant steric strain when it is in the plane of the ring, associated with the interaction of the ethyl group with the two carbonyl oxygens. This leads to calculated barriers of θ1 = 1469 cm-1 and θ1 = 1680 cm-1 in N-ethyl maleimide and N-ethyl succinimide, respectively.

Photophysical mechanism study of photophysical properties of new red BODIPY chromophores with or without methyl substitution

The relationship between the photophysical properties and structure of BODIPY derivatives always has attracted much attention. Two new BODIPY derivative chromophores with phenyl group substitutions at meso-/6- positions, with or without methyl substitutions at 1/3/5/7 positions were investigated by ways of combination of multiple experimental techniques and theoretical methods. The chromophore without methyl substitutions has a larger Stokes shift and better viscosity sensitivity compared to the other one. The intrinsic reason is that considerable charge transfer between the BODIPY core and the 6- position group is achieved in chromophore. However, this charge transfer process is severely weakened, if 1-/3-/5-/7- methyl substitutions existing, via restricting rotation between the core and side groups. At the same time, the non-radiative process is amplified significantly in chromophore without methyl substitution and the fluorescence efficiency decrease from 51.7% (with methyl substitutions) to 1.84% (without methyl substitutions) in DMSO. Quantum calculations indicate the presence or absence of methyl substitution can change both the shape and height of the torsional potential energy curve of the side groups, thereby affecting the fluorescence quantum yield and viscosity response performance of chromophores. Our work can provide foundation and ideas for designing and optimizing BODIPY derivatives with objective photophysical properties.

The theoretical study of the analytical potential energy functions, spectroscopic parameters and vibrational spectra of GeO molecules

Germanium oxide is an important optical dielectric material with high application value in integrated optical systems. In this paper, the potential energy curves (PECs) of the ground state (Χ1∑+) and three electron low-excited states (a3Σ+, A1Π and B3Π) of GeO molecules (a3Σ+, A1Π and B3Π) were calculated by using the Dunning's related harmonic basis function and large basis group aug-cc-pwCV5Z with diffusion groups. The analytical potential energy function was obtained by fitting the Murrell-Sorbie function (MS) and the least squares method, and the fitting error was very small, indicating that the obtained analytical potential energy function could reproduce the interaction between atoms in GeO molecules. The spectral constants calculated by using the obtained analytical potential energy function are in good agreement with the experimental values, indicating the reliability and accuracy of the obtained analytical potential energy function.

UNDULATING POTENTIALS OF RYDBERG Σ+-STATES OF ME-RG MOLECULES: NON-EMPIRICAL TREATMENT OF NA-HE EXCIPLEX

The multi-reference con guration interaction method based on single and double excitations (MR-CISD), l-independent core polarization potential (CPP) and diffuse function-saturated cc-pVQZ and aug-cc-pV5Z basis sets for Na and He atoms, respectively, have been used to perform non-relativistic calculations of potential energy curves and permanent dipole moment functions for the ground and excited electronic states of the exciplex Na-He molecule up to the Na(62S) state. The ab initio results obtained in a wide range of internuclear distances R [1.7, 20.0] (Å) have quantitatively claimed the undulating behavior of interatomic potentials, predicted within the framework of the inelastic scattering theory. It has been established that at large R the interatomic potentials and dipole moments of highly excited (3,6,10)2Σ+ states, converging to Na (n = 4, 5, 62S)+He(22S) atomic limits, are modulated by the nodal structure of the radial Rydberg wave function (n > 3) s-electron of Na atom during its scattering on the remote He atom.

Theoretical study on the atomic substitution effect on the aromaticity and ESIPT behavior of a novel chalcone-based fluorophore

Recently, a new ESIPT-based fluorophore (E)-2-(4-(dimethylamino) benzylidene)-7-hydroxy-1-indanone (7HIN) was designed and obtained experimentally. We investigated the excited state intramolecular proton transfer (ESIPT) behavior and photophysical properties of 7HIN based on density functional theory (DFT) and time-dependent DFT. Two derivatives of 7HIN (4HID and 4HBF) were obtained by replacing the CH2 group in the five-membered ring with NH group and O atom to study the atomic substitution effect on the proton transfer reactions and fluorescent features of 7HIN. All data from structural parameters, infrared frequencies and electron density showed that the intramolecular hydrogen bonds (IHB) in 7HIN and its derivatives were strengthened in the excited state (S1), which will accelerate the ESIPT process. The potential energy curves (PECs) indicated that the proton transfer can easily occur in the S1 state because of the lower energy barrier. The electron-hole analysis revealed that the S0 → S1 transition is an intramolecular charge transfer transition. The NH- and O-substitution led to a weakening of IHB, increased the ESIPT barrier and red-shifted the absorption/emission wavelength of 7HIN. The PBE38 functional in this work is very reliable since the experimental absorption/fluorescence wavelength of 7HIN was reproduced well.