Potential Energy Curves Research Articles

Improvement on the screening of nonlinear commutator operations in selective coupled-cluster using Lagrangian.

We introduce a Lagrangian implementation of the full coupled-cluster reduction [Xu et al., Phys. Rev. Lett. 121, 113001 (2018)], that is, a selected coupled-cluster (CC) based on an arbitrary-order full CC expansion using direct commutator expansions. In this method, the screening for the products of cluster amplitudes plays a central role to reduce the computational cost for the nonlinear commutator operations, while the convergence of the total energy in the standard energy expression is not rapid with tightening the threshold. The new implementation using Lagrangian is robust, containing error only quadratic to those of amplitudes, allowing a much larger screening threshold. We demonstrate the performance of the new implementation by investigating the calculations of N2 and C6H6. The accuracy and applicability are also demonstrated for the potential energy curve of H2O in comparison with conventional quantum chemical methods.

Assessing many-body methods on the potential energy surface of the (H2)2 hydrogen dimer.

The anisotropic potential energy surface of the (H2)2 dimer represents a challenging problem for many-body methods. Here, we determine the potential energy curves of five different dimer configurations (T, Z, X, H, and L) using the lattice regularized diffusion Monte Carlo method and a number of approximate functionals within density functional theory (DFT), including advanced orbital-dependent functionals based on the random phase approximation (RPA). We assess their performance in describing the potential wells, bond distances, and relative energies. The repulsive potential wall is studied by looking at the relative stability of the different dimer configurations as a function of an applied force acting along the intermolecular axis. It is shown that most functionals within DFT break down at finite compression, even those that give an accurate description around the potential well minima. Only by including exchange within RPA, a qualitatively correct description along the entire potential energy curve is obtained. Finally, we discuss these results in the context of solid molecular hydrogen at finite pressures.

A theoretical exploration of the influence of oxygen element on photo-induced behaviours for flavonoid derivatives with Me2N substitution

The exceptional properties of flavonoid derivatives are a great inspiration for our research. In the fields of medicine and chemistry, flavonoids present the superior ability to enhance non-specific immune function and humoral immune response. Herein, our primary focus lies in the theoretical exploration of the photo-induced characteristics exhibited by the novel Me2N-substituted flavonoid (MEF) fluorophore. Considering the potential photo-induced properties associated with chalcogen atomic electronegativity in photoexcitation, using density functional theory (DFT) and time-dependent DFT (TDDFT) methods, we primarily pay attention to probing into photo-induced hydrogen bonding effects and concomitant charge reorganisation processes. Given changes in chemical geometries and the infrared (IR) vibrational shifts of three MEF derivatives (MEF-O, MEF-S and MEF-Se), we confirm that intramolecular hydrogen bonding should be strengthened by facilitating excited state intramolecular proton transfer (ESIPT) reactions. Particularly, the redistribution of charge further shows the ESIPT behaviour. By constructing potential energy curves (PECs) and identifying transitional reaction state (TS) structures, we ultimately validate the electronegativity-dependent ESIPT mechanisms of chalcogen elements in MEF derivatives. We sincerely hope that our work can accelerate future development and applications of flavonoid derivatives.

Two-Positron-bonded Dihalides: Ps2XY (X, Y=F, Cl, Br).

This study explores the energetic stability and physical properties of complexes formed by two halide anions (X-, Y-=F-, X-, Br-), and two positrons (Ps: positron-electron pair). We combine electronic coupled cluster (CCSD(T)) calculations with positronic multicomponent renormalized partial third-order propagator (MC-REN-PP3) calculations to effectively recover correlation energies. Analysis of potential energy curves confirms the energetic stability of these positronic molecules, with optimized structures identified as global minima. Further investigation of electron and positron densities reveals stabilization owing to the formation of two-positron bonds. The global stability of the complexes contrasts with the metastable two-positron-bonded (PsH)2, which energetically favors the emission of Ps2. Comparative analysis of one- and two-positron dihalides indicates that the addition of a positron to PsXY- generally results in shorter bond distances, higher force constants, and lower dissociation energies, with exceptions due to differences in positron affinities of PsXY- and Y-. We explore the analogy between two-positron-bonded dihalide systems and two-electron-bonded dialkali molecules AB, (A, B=Na, K, Rb). The bonding properties in two-positron dihalides and their electronic dialkali analogs are comparable, displaying identical periodic trends. However, compared to their isoelectronic AB counterparts, the positron bonds in have shorter bond lengths, higher force constants, and higher bond energies.

Relationship between antioxidant activity and ESIPT process based on flavonoid derivatives: A comprehensive analysis

Antioxidant activity, as a topic of current interest, is discussed together with the excited state intramolecular proton transfer (ESIPT) process for three flavonoid derivatives, based on density functional theory (DFT)and time-dependent DFT (TD-DFT) methods, as well as DPPH free radical scavenging assay. The potential energy curves and transition states demonstrate that the three molecules can undergo only single proton transfer in the excited state, and all of them are ultrafast ESIPT processes. The absorption spectra of all the molecules show effective protection against UV radiation with low fluorescence intensity, especially Baicalein (Bai), which demonstrates their great potential for sunscreen applications. The density of states, HOMO energy values, global and local indices reveal that the antioxidant activity of the molecules after ESIPT process is enhanced, with Bai having the highest antioxidant activity, which is significantly attributed to the number and position of phenolic hydroxyl groups. Moreover, by comparing the DPPH free radical scavenging activity under the dark and UV radiation conditions, the radical scavenging activity (RSA) value in the UV radiation is remarkably higher than that in the dark condition, in which Bai achieves RSA value of 93.4%. Overall, the antioxidant activity of all three ESIPT-based flavonoid derivatives, especially Bai, is significantly elevated in the keto* form, which reinforces the significant relationship between antioxidant activity and ESIPT process, and provides new application prospects for molecules with ESIPT properties.

A static quantum embedding scheme based on coupled cluster theory.

We develop a static quantum embedding scheme that utilizes different levels of approximations to coupled cluster (CC) theory for an active fragment region and its environment. To reduce the computational cost, we solve the local fragment problem using a high-level CC method and address the environment problem with a lower-level Møller-Plesset (MP) perturbative method. This embedding approach inherits many conceptual developments from the hybrid second-order Møller-Plesset (MP2) and CC works by Nooijen [J. Chem. Phys. 111, 10815 (1999)] and Bochevarov and Sherrill [J. Chem. Phys. 122, 234110 (2005)]. We go beyond those works here by primarily targeting a specific localized fragment of a molecule and also introducing an alternative mechanism to relax the environment within this framework. We will call this approach MP-CC. We demonstrate the effectiveness of MP-CC on several potential energy curves and a set of thermochemical reaction energies, using CC with singles and doubles as the fragment solver, and MP2-like treatments of the environment. The results are substantially improved by the inclusion of orbital relaxation in the environment. Using localized bonds as the active fragment, we also report results for N=N bond breaking in azomethane and for the central C-C bond torsion in butadiene. We find that when the fragment Hilbert space size remains fixed (e.g., when determined by an intrinsic atomic orbital approach), the method achieves comparable accuracy with both a small and a large basis set. Additionally, our results indicate that increasing the fragment Hilbert space size systematically enhances the accuracy of observables, approaching the precision of the full CC solver.

Quantum Chemical Model Calculations of Adhesion and Dissociation between Epoxy Resin and Si-Containing Molecules.

There is no doubt that when solid surfaces are modified, the functional groups and atoms directly bonded to solid atoms play a major role in adsorption interactions with molecules or resins. In this study, the adhesion and dissociation between epoxy resin and molecules containing Si atoms were analyzed. The analysis, conducted in contact with the solid surface of silicon, utilized quantum chemical calculations based on a molecular model. We compared some Si-containing molecular models to test quantum chemical calculations that contribute to the study of adhesion and dissociation between epoxy resins and solid surfaces somehow other than simple potential energy curve calculations. The AFIR (artificial force induced reaction) method, implemented in the GRRM (global reaction route mapping) program, was employed to separate an epoxy resin model molecule and three types of silicon compounds (Si(CH3)2(OH)2, Si(CH3)4, and (CH3)2SiF2) in three directions, determining their minimum dissociation energy when changing the applied energy by 2.5 kJ/mol. In systems with weak hydrogen bonds, such as Si(CH3)4 or (CH3)2SiF2, the energy required for dissociation was not large; however, in systems with strong hydrogen bonds, such as Si(CH3)2(OH)2, dissociation was more difficult in the vertical direction. Although anisotropy due to hydroxyl groups was calculated in the horizontal direction, dissociation remained relatively easy.

Multireference Fock Space Coupled-Cluster Method for the (3,0) Sector.

This work reports an implementation of a novel realization of the multireference coupled cluster theory formulated in Fock space. Extending the previous formulation carried out in the (1,1) [M. Musial, R. J. Bartlett, J. Chem. Phys. 129, 044101 (2008)], (0,2) [M. Musial, R. J. Bartlett, J. Chem. Phys. 135, 044121 (2011)], and (2,0) [M. Musial, J. Chem. Phys. 136, 134111 (2012)] sectors to the (3,0) sector, we are able to treat structures with three valence electrons. The (3,0) sector describes systems with three electrons added to the reference, which means that in order to perform correlated calculations for the neutral AB molecule, we have to adopt as the reference a triply ionized structure AB3+. A desirable situation occurs when such an ion has a closed-shell structure and also dissociates into closed shell fragments. This feature makes it possible to apply the restricted Hartree-Fock scheme for the whole range of interatomic distances. Examples of molecules of this type are the diatomics formed by the atoms of alkali metals and alkaline earth metals. An analogous structure is also exhibited by alkali metal monocarbides. In the current work, we have calculated the potential energy curves and spectroscopic constants for the LiBe, LiC, and NaC molecules.

Phenol Photostatic Spectra and Quantum‐Classical Photodynamic Deprotonation

ABSTRACTThe spectral‐luminescence properties and photochemical conversions of phenol were analyzed for an isolated molecule as well as in water solvents in a continuum implicit model and explicit atomistic surroundings. This involved employing cut‐edge hybrid quantum‐classical methodologies to generate static optical spectra and the excited dissipative crossing potential energy curves. A combination of electronic excitations, gradient calculations, and embedding electrostatic potential fitting charges on quantum‐classical molecular dynamic propagation trajectories provided statistically averaged absorption spectra. The mixed‐reference spin‐flip multiconfigurational linear response method based on reference triplet preprocessed in the time‐dependent density‐functional theory was utilized to determine conical intersections between the lowest excited and ground states, as well as two‐stage transitions from the second excitation to the ground state. Non‐adiabatic quantum‐classical molecular dynamics defined photodissipative trajectories of excited states, their lifetimes, and crossing points through trajectory surface hopping together with the mixed‐reference spin‐flip and embedding electrostatic potential fitting approaches. Dyson orbitals of the extended Koopmans' theorem were applied to reveal the nature of molecular states at conical intersections and key points on photodynamic trajectories. Potential hydroxyl group cleavage predicted with conical intersections searching turns to “swift” OH deprotonation through |π→⟩ transition along photodynamic propagations in contrast with “long” processes leading to benzene ring deformation with stable OH bond.

Direct observation of the twisted intramolecular charge-transfer state in polycyclic purinium salts.

Based on femtosecond transient absorption spectroscopy (fs-TAS) of 3-methyl-7,8-diphenyl-3H-purino[6,1-a] isoquinolin-6-ium trifluoromethanesulfonate in dimethyl sulfoxide (DMSO), the stimulated emission (SE) signal redshifts from 400 to 500 nm in 4.8 ps. In a glycerol/DMSO mixed solution, when the glycerol content is 25% and 50%, the delay is extended to 6.9 and 68 ps, respectively. The theoretical emission spectrum in the scanning of potential energy curves demonstrates that the rotation of the φ2 with a lower energy barrier (16.1 kcal/mol) occurs prior to that of φ1. In addition, the purinium salt molecule has a twisted intramolecular charge transfer (TICT) process occurring from the locally excited (LE) state to the charge transfer (CT) state, and torsion of φ2 is restrained in high-viscosity environments, which induces the redshift of SE and its increasing lifetime.

Ground and Excited Electronic Structure Analysis of FeH with Correlated Wave Function Theory and Density Functional Approximations.

FeH is one of the most challenging diatomic molecules to study under electronic structure theory. Here, we have successfully studied 22 electronic states of FeH using ab initio multireference configuration interaction (MRCI), Davidson-corrected MRCI (MRCI+Q), and coupled cluster singles, doubles, and perturbative triples [CCSD(T)] levels of theory. We report their potential energy curves (PECs), excitation energies, dissociation energies, equilibrium electronic configurations, and a series of spectroscopic constants with the use of augmented triple-ζ, quadruple-ζ, and quintuple-ζ quality correlation consistent basis sets. The scalar relativistic effects and active space and core electron correlation contribution on the properties of FeH are also explored. The use of a large CASSCF active space that includes 4s, 4p, 3d, and 4d orbitals of Fe and the 1s of H is critical for producing accurate full PECs with proper dissociations and predicting the exact order of the electronic states. Our findings are in harmony with the experimental results available in the literature and will serve as reference values for future studies of FeH. Furthermore, with the use of PECs, the total internal partition function sum (TIPS) of FeH was calculated across a range of temperatures. Finally, we exploited the single-reference nature of the a6Δ of FeH and its ionized product FeH+ (X5Δ) to evaluate the associated density functional theory (DFT) errors on their dissociation energies and spectroscopic parameters.

Theoretical study on the spectroscopic and transition properties of phosphorus dimer cation

The potential energy curves of 18 Λ-S states of the P2 + cation have been constructed using the internally contracted multi-reference configuration interaction approach combined with the Davidson correction. The basis-set extrapolation to the complete basis set limit is performed. The relativistic effect is considered in calculations. Treatment of scalar relativistic effect at the third-order Dkroll-Hess approximate and spin-orbit coupling with the state-average Breit-Pauli operator is made. Based on the obtained potential energy curves, the spectroscopic parameters for all bound Λ-S and Ω states are determined. These results are in agreement with experiment where the spectroscopic data are available. The transition dipole moments are calculated. The properties of the dipole-allowed transitions among doublet or quartet Λ-S states are evaluated, from which Einstein coefficients, Franck-Condon factors and radiative lifetimes are estimated. The spin-orbit coupling effect on the transition properties of the 12Πg→X2Πu system is also studied. The spectroscopic and transition properties reported in this study can be used to guide the detection of phosphorus dimer cation in spectroscopy experiments.

Theoretical spin-orbit laser cooling for AlZn molecule.

A spin-orbit coupling electronic structure study of the AlZn molecule is conducted to investigate the molecular properties of the low-lying electronic states and their feasibility toward direct laser cooling. This study uses the complete active-space self-consistent field level of theory, followed by the multireference configuration interaction method with Davidson correction (+Q). The potential energy and dipole moment curves and the spectroscopic constants are computed for the low-lying doublet and quartet electronic states in the 2S+1Λ± and Ω(±) representations. The transition dipole moments, the Franck-Condon factors, the Einstein coefficient, the radiative lifetimes, the vibrational branching ratio, and the slowing distance are determined between the lowest spin-orbit bound electronic states. These results show that the molecule AlZn has a high potential for laser cooling through the X2Π1/2 → (2)2Π1/2 transition by utilizing four lasers at a wavelength in the ultraviolet region, reaching a sub-microkelvin temperature limit.

Study of the Energy Crossing Between Excited States Affected by the Electronegativity of Substituents for Three 4-Azido-1,8-naphthalimide Derivatives.

Rapid detection of H2S is crucial for human physiological health and natural ecosystems. In this study, the fluorescent sensing mechanisms of three 4-azido-1,8-naphthalimide-based fluorescent probes to monitor H2S were theoretically investigated by density functional theory and time-dependent density functional theory. The potential energy curve of the charge transfer (CT) state has a crossover with that of the locally excited (LE) state proved by the constructed linear interpolating internal coordinate pathway. Thus, the transform takes place from the LE state to the CT state causing the fluorescence quenching of the probes from a nonradiative transition process of the CT state. The distance between the Franck-Condon point and the minimal energy conical intersection becomes larger with the increase of the electronegativity of substituents on the 1,8-naphthalimide fluorophore. In addition, the degree of charge separation is closely related to the energy difference between the CT and the LE states which are also essentially affected by the electronegativity of the substituents. Since the electronegativity of the substituents has proved important for the probes, our work lays a certain theoretical foundation for the design and synthesis of more sensitive 4-azido-1,8-naphthalimide-based fluorescent probes.

Molecular line lists for the singlet states in gaseous YN at high temperature

ABSTRACT Our aim in this study is to investigate the electronic structure of the gaseous YN molecule and provide an accurate molecular line list of spectroscopic transitions between the five lowest singlet states. The calculations were done by using large basis set for yttrium aug-cc-pVQZ-PP with relativistic effective core potentials at the spin-free level. We first used the method of complete active space self-consistent field, which was followed by the multireference singles and doubles configuration interaction. Potential energy curves and permanent and transition dipole moments were calculated at the internuclear distance range of 1.3–2.96 Å. For each state, we calculated the spectroscopic constants (Te, ωe, ωexe, ωeye, Be, αe, Re). The calculated values of the spectroscopic constants are in excellent agreement with the experimental constants available, with a relative difference of less than 5 cm−1. We further calculated the transition intensities of allowed transitions, and we provided the absorption spectra up to a temperature of 4000 K. The computed molecular line list contains 2.6 million transitions calculated between almost 18 186 vibro-rotational energy levels. It covers the frequency range between 0 and 30 000 cm−1. The effect of temperature on the spectra of hot YN was investigated with partition functions calculated between 298 and 4000 K. This study should help in identifying the singlet state spectrum of the hot YN molecule, which is possibly found in the atmospheres of cool stars and hot rocky super-Earths.

Programmable Supratransmission in a Mechanical Chain with Tristable Oscillators

Abstract Supratransmission refers to a phenomenon that nonlinear medium allows large-amplitude waves to transmit energy through the band gap, which has been extensively studied in many nonlinear models. Recently, controlling supratransmission using bistable nonlinearities has gained growing attentions. Nevertheless, the general principles of controlling supratransmission using multistable nonlinearities have remained elusive. As a first step to address such challenge, this work presents programmable supratransmission using tristable nonlinearities. Through numerical simulations, we demonstrate that a mechanical chain consisting of tristable oscillators can achieve rich programmable features of supratransmission by simply tuning the tristable potential energy curve, providing new insights into how supratransmission can be controlled. The current work deepens the understanding of programmable supratransmission using multistable nonlinearities.

Nondynamical correlation effects in multidimensional potential energy curves of prototypical hydrocarbons

We demonstrate that simultaneously stretching all bonds in a molecule by small increments provides a systematic approach to gradually increasing its multireference character. We show this for four hydrocarbons — methane, ethane, ethylene, and acetylene — each representing a progressively more complex electronic structure. The J1, D1, and %TAE[(T)] multireference diagnostics increase as all the bonds are stretched simultaneously. The post-CCSD(T) correlation components of the total atomization energy (TAE) up to CCSDTQ systematically increase as the bonds are stretched. The extent of the increase in the multireference character correlates with the complexity of the electronic structure in the order methane → ethane → ethylene → acetylene. The CCSDTQ/CBS multidimensional potential energy curves serve as benchmarks for assessing the performance of DFT methods for strong correlation effects. The conventional DFT methods B97-D, TPSS, and TPSSh and double-hybrid DFT methods are more robust toward multireference effects.

Net emission coefficient of magnesium oxide crystal arc plasma with different Mg particle concentrations

The aim of the present study was to construct a molecular spectral database of magnesium oxide crystal arc plasma, thereby allowing for the net emission coefficient of arc to be calculated at different temperatures, pressures and Mg ratios. First, Rydberg-Klein-Rees inversion method was adopted to reconstruct the potential-energy curves of diatomic molecules. Subsequently, the Schrödinger equation was solved to determine the molecular wave function. This solution combined with the electrical transition moment function facilitates the calculation of radiative transition probabilities between different energy levels and the development of this database. Second, calculation models of the bound-free and free-free radiative absorption cross-section were established and use to calculate the continuous radiation of atoms. Finally, the radiative capability of different particles was calculated separately, followed by calculation of the net emission coefficient of plasma through addition The experimental results reveal that the net emission coefficient of air plasma under atmospheric pressure is consistent with existing research in both its magnitude and trend. Given that Mg can be ionized at lower temperatures, the magnesium oxide crystal arc plasma exhibited a pronounced radiative capacity at these temperatures. Additionally, a larger optical transmission distance corresponded to a reduced net emission coefficient of the plasma.

Quantum Algorithms for the Variational Optimization of Correlated Electronic States with Stochastic Reconfiguration and the Linear Method.

Solving the electronic Schrodinger equation for strongly correlated ground states is a long-standing challenge. We present quantum algorithms for the variational optimization of wave functions correlated by products of unitary operators, such as Local Unitary Cluster Jastrow (LUCJ) ansatzes, using stochastic reconfiguration (SR) and the linear method (LM). While an implementation on classical computing hardware would require exponentially growing compute cost, the cost (number of circuits and shots) of our quantum algorithms is polynomial in system size. We find that classical simulations of optimization with the linear method consistently find lower energy solutions than with the L-BFGS-B optimizer across the dissociation curves of the notoriously difficult N2 and C2 dimers; LUCJ predictions of the ground-state energies deviate from exact diagonalization by 1 kcal/mol or less at all points on the potential energy curve. While we do characterize the effect of shot noise on the LM optimization, these noiseless results highlight the critical but often overlooked role that optimization techniques must play in attacking the electronic structure problem (on both classical and quantum hardware), for which even mean-field optimization is formally NP hard. We also discuss the challenge of obtaining smooth curves in these strongly correlated regimes, and propose a number of quantum-friendly solutions ranging from symmetry-projected ansatz forms to a symmetry-constrained optimization algorithm.

Rydberg-State Double-Well Potentials of Van der Waals Molecules

Recent progress in studies of Rydberg double-well electronic energy states of MeNg (Me = 12-group atom, Ng = noble gas atom) van der Waals (vdW) molecules is presented and analysed. The presentation covers approaches in experimental studies as well as ab initio-calculations of potential energy curves (PECs). The analysis is shown in a broader context of Rydberg states of hetero- and homo-diatomic molecules with PECs possessing complex ‘exotic’ structure. Laser induced fluorescence (LIF) excitation spectra and dispersed emission spectra employed in the spectroscopical characterization of Rydberg states are presented on the background of the diverse spectroscopic methods for their investigations such as laser vaporization–optical resonance (LV-OR), pump-and-probe methods, and polarization labelling spectroscopy. Important and current state-of-the-art applications of Rydberg states with irregular potentials in photoassociation (PA), vibrational and rotational cooling, molecular clocks, frequency standards, and molecular wave-packet interferometry are highlighted.