Energy Isomers Research Articles

Reactivity of arsenoplatin complex versus water and thiocyanate: a DFT benchmark study

Seven different density functionals, including GGAs, meta-GGAs, hybrids and range-separated hybrids, and considering Grimme’s empirical dispersion correction (M06-L, M06-2X, PBE0, B3LYP, B3LYP-D3, CAM-B3LYP, ωB97X) have been tested for their performance in the prediction of molecular structures, energies and energy barriers for a class of newly developed antitumor platinum complexes involving main group heavy elements such as arsenic. The calculated structural parameters, energies and energy barriers have been compared to the available experimental data. The results show that range-separated hybrid functionals CAM-B3LYP and ωB97X give good results in predicting both geometrical parameters and isomerization energies and barrier heights and are promising new tools for the theoretical study of novel platinum(II) arsenic compounds.

Towards Near-Exact Solutions of Molecular Electronic Structure: Full Coupled-Cluster Reduction with a Second-Order Perturbative Correction.

We introduce a new augmented adaptation of the recently developed full coupled-cluster reduction (FCCR) with a second-order perturbative correction, abbreviated as FCCR(2). FCCR is a selected coupled-cluster expansion aimed at optimally reducing the excitation manifold and commutator expansions for high-rank excitations for obtaining accurate solutions of the electronic Schödinger equation in a size-extensive manner. The present FCCR(2) enables estimating the residual correlation of FCCR by the second-order perturbative correction E(2) from the complementary space of the FCCR projection manifold. The linear relationship between E(2) and the energy of FCCR(2) allows accurate estimates of near-exact energies for a wide variety of molecules with strong electron correlation. The potential of the method is demonstrated using challenging cases, the ground-state electronic energy of the benzene molecule in equilibrium and stretched geometries, and the isomerization energy of the transition metal complex [Cu(NH3)]2O22+.

Quantum chemical calculation of intrinsic reaction coordinates from trans to cis structure of fluvoxamine

Fluvoxamine is a selective serotonin reuptake inhibitor. Its trans-isomer [(E)-isomer] is pharmacologically active, whereas its cis-isomer [(Z)-isomer] loses its activity. It is a pharmaceutical interest whether the structural change from the (E)-isomer to the (Z)-isomer spontaneously occurs in aqueous solutions without ultraviolet (UV) irradiation. In the present study, the transition state of fluvoxamine was determined by quantum chemical calculation using density functional theory (DFT), and the intrinsic reaction coordinates (IRCs) from the (E)-isomer to the (Z)-isomer were calculated using UB3LYP/6-311++G(d,p) with the integral equation formalism-polarizable continuum model (IEF-PCM). The activation energy of isomerization from the (E)-isomer to the (Z)-isomer was estimated to be 55 kcal/mol. Further, the absorption spectra, the nuclear magnetic resonance chemical shift values, the Raman spectra and the infrared spectra were calculated for the (E) and (Z)-isomers obtained from the reaction coordinate calculation, and these results were in good agreement with the experimental values. The geometrical structures of the (E) and (Z)-isomers proposed in the present study can be used as theoretical models of fluvoxamine for molecular dynamics calculations in future.

Measurement of the ^{229}Th Isomer Energy with a Magnetic Microcalorimeter.

We present a measurement of the low-energy (0-60keV) γ-ray spectrum produced in the α decay of ^{233}U using a dedicated cryogenic magnetic microcalorimeter. The energy resolution of ∼10 eV, together with exceptional gain linearity, allows us to determine the energy of the low-lying isomeric state in ^{229}Th using four complementary evaluation schemes. The most precise scheme determines the ^{229}Th isomer energy to be 8.10(17)eV, corresponding to 153.1(32)nm, superseding in precision previous values based on γ spectroscopy, and agreeing with a recent measurement based on internal conversion electrons. We also measure branching ratios of the relevant excited states to be b_{29}=9.3(6)% and b_{42}<0.7%.

Spectroscopic study of magnesium dinitrogen and sodium dinitrogen cation

ABSTRACT Despite its likely importance in astrochemistry, pure rotational spectra are not observable for gas-phase N2 since this molecule has no permanent dipole moment. Complexation of monomeric N2 with a cationic metal (MN2+) may be kinetically and thermodynamically favourable, and the detection of such MN2+ molecules could be useful tracers of N2 in order to probe its abundance and kinetics. Highly accurate quartic force field methods have been applied here to compute rotational and vibrational spectroscopic properties of the NaN2+ and MgN2+ molecules via a coupled cluster-based composite approach with additional corrections for post-CCSD(T) electron correlation and relativistic effects. The relative energies of various isomers have also been computed and show that both NaN2+ and MgN2+ have linear ground electronic states. At the highest level of theory, rotational constants (B0) of 4086.9 and 4106.0 MHz are predicted for NaN2+ and MgN2+, respectively, with dipole moments of 6.92 and 4.34 D, respectively, making them rotationally observable even at low concentrations. Post-CCSD(T) electron correlation corrections lower the N–N stretching frequency while relativistic corrections have a much smaller effect putting the fundamental frequencies at 2333.7 and 2313.6 cm−1, respective of NaN2+ and MgN2+ slightly above that in N2H+. Additive corrections do not significantly change the other two vibrational modes. An anharmonic, zero-point corrected N2 dissociation energy of 7.3 and 7.0 kcal mol−1 is, respectively, reported for NaN2+ and MgN2+ suggesting possible formation of these molecules in protoplanetary discs or planetary nebulae that are metal- and nitrogen-rich.

An accurate 5D potential energy surface for H3O+-H2 interaction.

Modeling of the observational spectra of H3O+ allows for a detailed understanding of the interstellar oxygen chemistry. While its spectroscopy was intensively studied earlier, our knowledge about the collision of H3O+ with the abundant colliders in the interstellar medium is rather limited. In order to treat these collisional excitation processes, it is first necessary to calculate the potential energy surface (PES) of the interacting species. We have computed the five-dimensional rigid-rotor PES of the H3O+-H2 system from the explicitly correlated coupled-cluster theory at the level of singles and doubles with perturbative corrections for triple excitations [CCSD(T)-F12] with the moderate-size augmented correlation-consistent valence triple zeta (aug-cc-pVTZ) basis set. The well depth of the PES is found to be rather large, about 1887.2 cm-1. The ab initio potential was fitted over an angular expansion in order to effectively use it in quantum scattering codes. As a first application, we computed dissociation energies for the different nuclear spin isomers of the H3O+-H2 complex.

Largest molecular quantum computation performed

Researchers have used a quantum computer to model the electronic energy of diazene isomerization ( 2020, DOI: ). The scientists and other experts say the demonstration will be a building block for ...

Accurate Many-Body Repulsive Potentials for Density-Functional Tight Binding from Deep Tensor Neural Networks.

We combine density-functional tight binding (DFTB) with deep tensor neural networks (DTNN) to maximize the strengths of both approaches in predicting structural, energetic, and vibrational molecular properties. The DTNN is used to construct a nonlinear model for the localized many-body interatomic repulsive energy, which so far has been treated in an atom-pairwise manner in DFTB. Substantially improving upon standard DFTB and DTNN, the resulting DFTB-NNrep model yields accurate predictions of atomization and isomerization energies, equilibrium geometries, vibrational frequencies, and dihedral rotation profiles for a large variety of organic molecules compared to the hybrid DFT-PBE0 functional. Our results highlight the potential of combining semiempirical electronic-structure methods with physically motivated machine learning approaches for predicting localized many-body interactions. We conclude by discussing future advancements of the DFTB-NNrep approach that could enable chemically accurate electronic-structure calculations for systems with tens of thousands of atoms.

Concepts for direct frequency-comb spectroscopy of 229mTh and an internal-conversion-based solid-state nuclear clock

A new concept for narrow-band direct nuclear laser spectroscopy of $^{229\text{m}}$Th is proposed, using a single comb mode of a vacuum ultraviolet frequency comb generated from the 7th harmonic of an Yb-doped fiber laser system. In this concept more than $10^{14}$ $^{229}$Th atoms on a surface are irradiated in parallel and a successful nuclear excitation is probed via the internal-conversion (IC) decay channel. A net scanning time of 15 minutes for the most recent 1~$\sigma$ energy uncertainty interval of 0.34 eV appears to be achievable when searching for the nuclear transition. In case of successful observation, the isomer's energy value would be constrained to an uncertainty of about 100~MHz, which is a factor of $10^6$ of improvement compared to today's knowledge. Further, the comb mode could be stabilized to the nuclear transition using the same detection method, allowing for the development of an IC-based solid-state nuclear clock, which is shown to achieve the same performance as a crystal-lattice nuclear clock, however, with the advantage of a drastically simpler detection scheme. Finally, it is shown that the same laser system could be used to narrow down the isomer's transition energy by further six orders of magnitude during laser excitation of $^{229}$Th$^{3+}$ ions in a Paul trap and to drive nuclear Rabi oscillations, as required for the development of a nuclear clock based on a single $^{229}$Th$^{3+}$ ion.

Conformers of dehydrogenated glycine isomers.

We report a comprehensive ab initio investigation of the conformers of dehydrogenated glycine radicals using the STO-3G, 3-21G, and aug-cc-pVDZ (aVDZ) basis sets and the UHF and UMP2 (H2 N-CH-COOH and HN-CH2 -COOH) as well as MCSCF and MRCI (H2 N-CH2 -COO) methods via two different conformational search strategies generating initial structures for optimizations by (a) removing H atoms from glycine conformers and (b) scanning torsional angles describing internal rotation along the CC, CN, and CO (except for H2 N-CH2 -COO) bonds of the radicals. We find four H2 N-CH-COOH {InCH , IInCH , IIInCH , IVnCH } and seven HN-CH2 -COOH {IpNH , IIpNH , IIInNH , IVpNH VnNH , VIpNH , VIIpNH } conformers with classical(adiabatic) relative energies of {0.00(0.00), 1.57(1.55), 5.25(5.03), 9.85(9.72)} and {0.00(0.00), 0.78(1.06), 1.93(2.08), 3.34(3.16), 3.39(3.29), 5.00(4.86), 9.27(8.87)} kcal/mol, respectively, obtained with UCCSD(T)-F12b/aug-cc-pVTZ(+UCCSD(T)-F12b/aVDZ ZPE correction) and four H2 N-CH2 -COO {IpCOO , IInCOO , IIIpCOO , IVnCOO } conformers with MRCI-F12+Q/aVDZ(+MRCI/aVDZ ZPE correction) energies of {0.00(0.00), 1.65(1.64), 1.78(1.75), 2.21(2.21)} kcal/mol, where n and p denote C1 and Cs symmetry. The MRCI-F12+Q[UCCSD(T)-F12b] InCH → IpNH and InCH → IpCOO classical(adiabatic) isomerization energies are 18.51(17.32)[21.20(20.01)] and 31.88(31.66) kcal/mol, respectively.

Probing the ionization potentials of the formaldehyde dimer.

In this work, we present a computational investigation on the ionization potentials (IPs) of the formaldehyde dimer, (H2CO)2. Twelve lowest lying IPs (corresponding to the entire valence orbitals) for both C2h and Cs symmetry conformers have been computed at the coupled cluster level of theory using large correlation consistent basis sets with extrapolation to the complete basis set limit and consideration of core electron correlation effects. Specifically, the equation-of-motion ionization potential coupled-cluster with single and double (EOMIP-CCSD) excitations method with the aug-cc-pVXZ and aug-cc-pCVXZ (X = T, Q, and 5) basis sets combined with the Feller-Peterson-Dixon approach was employed, as well as CCSD with perturbative triples [CCSD(T)] with the aug-cc-pVTZ basis sets. In general, excellent agreement was observed from the comparison between the results obtained through the use of these approaches. In addition, the IPs for the formaldehyde monomer were also obtained using such methodologies and the results compared with existing experimental data; excellent agreement was also observed in this case. To the best of our knowledge, this work represents the first of its kind to determine the IPs for all these systems using a high level theory approach and is presented to motivate experimental investigations, e.g., studies involving photoionization, particularly for the formaldehyde dimer. The equilibrium binding energy of the C2h dimer is calculated in this work at the CCSD(T)/aug-cc-pVTZ level of theory to be -4.71 kcal/mol. At this same level of theory, the equilibrium isomerization energy between C2h and Cs conformers is 0.76 kcal/mol (Cs conformer being more stable).

Mol-ecular and crystal structure, lattice energy and DFT calculations of two 2'-(nitro-benzo-yloxy)aceto-phenone isomers.

The two isomers 2'-(4-nitro-benzo-yloxy)aceto-phenone (systematic name: 2-acetyl-phenyl 4-nitro-benzoate) (I) and 2'-(2-nitro-benzo-yloxy)aceto-phenone (systematic name: 2-acetyl-phenyl 2-nitro-benzoate) (II), both C15H11NO5, with para and ortho positions of the nitro substituent have been crystallized and studied. It is evident that the variation in the position of the nitro group causes a significant difference in the mol-ecular conformations: the dihedral angle between the aromatic fragments in the mol-ecule of I is 84.80 (4)°, while that in the mol-ecule of II is 6.12 (7)°. Diffraction analysis revealed the presence of a small amount of water in the crystal of I. DFT calculations of the mol-ecular energy demonstrate that the ortho substituent causes a higher energy for isomer II, while crystal lattice energy calculations show that the values are almost equal for two isomers.

Electronic Bridge Excitation in Highly Charged ^{229}Th Ions.

The excitation of the 8eV ^{229m}Th isomer through the electronic bridge mechanism in highly charged ions is investigated theoretically. By exploiting the rich level scheme of open 4f orbitals and the robustness of highly charged ions against photoionization, a pulsed high-intensity optical laser can be used to efficiently drive the nuclear transition by coupling it to the electronic shell. We show how to implement a promising electronic bridge scheme in an electron beam ion trap starting from a metastable electronic state. This setup would avoid the need for a tunable vacuum ultraviolet laser. Based on our theoretical predictions, determining the isomer energy with an uncertainty of 10^{-5} eV could be achieved in one day of measurement time using realistic laser parameters.

Absorption and emission properties of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (M = Al, Ga, In) and correlations with molecular electrostatic potential.

Substituent effect for a series of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (Mq3) of aluminum, gallium, and indium are investigated using density functional theory (DFT) for the ground state properties and the time-dependent version of DFT (TDDFT) for their absorption and emission properties. A comparison between the ground state energy of mer and fac isomers of all the complexes revealed that the mer configuration is always more stable than fac. The substituent effect is significantly reflected at the fluorescence maximum (λF ) values whereas the effect is moderate at the absorption maximum (λabs ) values. The molecular electrostatic potential (MESP) at the metal center (VM ) and the most electron rich region indicated by MESP minimum (Vmin ), located at the oxygen of phenoxide ring exhibit excellent correlations with the λF and Stokes shift (λF -λabs ) values. The study suggests the use of Stokes shift as an experimental quantity to measure the excited state substituent effect while the Vmin or VM emerge as theoretical quantities to measure the same.

Electron correlation effects in isomers of C20

The C20 molecule exists as three low-energy isomers: the monocyclic ring, a corannulene-like bowl structure, and the cage-the smallest possible fullerene. The curious structures of these isomers, along with the valuable properties and possible applications of fullerenes more generally, mean that C20 has attracted interest both experimentally and computationally. Unfortunately, previous theoretical studies have found these C20 isomers present a significant computational challenge, and widely used methods such as Density Functional Theory with different functionals have been unable to agree on even the relative ordering of the isomer energies. Even accurate high-level methods such as coupled-cluster with singles, doubles, and perturbative triples (CCSD(T)) and Diffusion Monte Carlo (DMC) have previously disagreed on the energetic ordering of these isomers. Here we re-examine the ring, bowl, and cage isomers of C20 using a more accurate DMC technique. We employ a novel method to go beyond the single-determinant DMC approaches previously used, and instead use more accurate multi-determinant trial wavefunctions. Our results show that the fullerene cage exhibits different electron correlation effects than the ring and bowl, which when taken into account leads to a reordering of their relative energies. This finally establishes agreement between DMC and relatively recent complete-basis CCSD(T) results, thereby resolving a long-standing disparity between these two high-level descriptions of the C20 isomers. The approach we use is generalisable, and could be used to provide insight into even larger systems in future.

DFT calculation of 229thorium-doped magnesium fluoride for nuclear laser spectroscopy

The 229thorium nucleus has an extremely low-energy isomeric state that could be manipulated with light in the vacuum ultraviolet (VUV) range. Recent measurements based on internal conversion electrons place the isomer energy at 8.28(17) eV (Seiferle B et al 2019), within the transmission window of large-band-gap materials, such as fluoride single crystals. Doping 229Th into VUV-transparent materials realizes a spectroscopy target with a high nuclei density and might form the basis of a solid-state nuclear clock. This paper presents a theoretical study of the optical properties of a thorium-doped MgF2 crystal. Using the Vienna Ab-initio Simulation Package, we perform density functional theory calculations of the electronic and optical properties of Th:MgF2. We determine whether thorium will be accepted as a dopant and identify the charge compensation mechanism and geometry. The simulations indicate, that the band gap of Th-doped MgF2 will be significantly reduced compared to undoped MgF2, below the expected 229Th isomer energy. This result is in striking contrast to a similar study performed for Th-doped CaF2 (Dessovic P et al 2014 J. Phys. Condens. Matter 26 105402).

Molecular Engineering of Cyano‐Substituted Carbazole‐Based Host Materials for Simultaneous Achievement of High Efficiency and Long Lifetime in Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractA series of isomeric high triplet energy host materials named 1CNCzBN, 2CNCzBN, 3CNCzBN, and 4CNCzBN containing a cyanocarbazole and a benzonitrile for blue phosphorescent organic light‐emitting diodes (PhOLEDs) is presented. The effect of the substitution position of the cyano unit in the carbazole core on physicochemical and electroluminescence characteristics is described. All the compounds show high triplet energy (ET) of above 2.85 eV and the 3CNCzBN compound containing the cyano unit at C3 position of carbazole exhibits superior ET of 3.04 eV. Except for 1CNCzBN, all the compounds reveal good electron‐transporting properties, evidenced by the single carrier device analysis. Furthermore, the applicability of these compounds as electron‐transport‐type host materials for blue PhOLEDs is tested by employing a blue phosphor and the blue PhOLEDs exhibit high EQE over 20%. Among the compounds, the 3CNCzBN‐based device exhibits excellent performance with maximum external quantum efficiency (EQE) of 25.6% and current efficiency (CE) of 52.1 cd A−1. Importantly, all the compounds reveal excellent operational stability with long lifetime and the 3CNCzBN device displays superior lifetime of 20 h up to 70% of its initial luminance (L0 = 1000 cd m−2). It is believed that this study will provide fundamental insights to develop highly efficient cyano featured carbazole‐based host materials for blue PhOLEDs with superior EQE and long lifetime.

Assessment of second-order Møller-Plesset perturbation theory for isomerization and dissociation energies of nitramide

Based on the optimized molecular geometries at the B3LYP/cc-pVDZ level, the electronic and nuclear repulsion energies of nitramide (NH2NO2), O-nitrosohydroxylamine (NH2ONO), 1-hydroxydiazene 1-oxide (NH=N(O)OH), the transition state between NH2NO2 and NH2ONO, the transition state between NH2NO2 and NH=N(O)OH, NH2 radical, NO2 radical, H2O, N2O, H2, N2, O2, H, N and O were calculated by various second-order Møller–Plesset perturbation theory (MP2) methods. The domain based local pair natural orbital (DLPNO), explicitly correlated F12, density fitting (RI), spin-component scaled (SCS) and orbital optimized (OO) calculations were employed in MP2 calculations. The isomerization and dissociation energies of NH2NO2 were estimated by CCSD(T)-F12-RI as benchmark method. The testing results indicate that the deviations can be reduced by SCS method efficiently.

Development of Density Functional Tight-Binding Parameters Using Relative Energy Fitting and Particle Swarm Optimization.

We provide a strategy to optimize density functional tight-binding (DFTB) parameterization for the calculation of the structures and properties of organic molecules consisting of hydrogen, carbon, nitrogen, and oxygen. We utilize an objective function based on similarity measurements and the Particle Swarm Optimization (PSO) method to find an optimal set of parameters. This objective function considers not only the common DFTB descriptors of binding energies and atomic forces but also incorporates relative energies of isomers into the fitting procedure for more chemistry-driven results. The quality in the description of the binding energies and atomic forces is measured based on the Ballester similarity index and relative energies through a similarity index induced by the Levenshtein edit distance to quantify the correct energetic order of isomers. Training and testing datasets were created to include all relevant chemical functional groups. The accuracy of this strategy is assessed, and its range of applicability is discussed by comparison against our previous parameterization [A. Krishnapriyan, et al., J. Chem. Theory Comput. 13, 6191 (2017)]. The improved performance of the new DFTB parameterization is validated with respect to the density functional theory large datasets QM-9 [R. Ramakrishnan, et al., Sci. Data 1, 140022 (2014)] and ANI-1 [J. S. Smith, et al., Sci. Data 4, 170193 (2017)], where excellent agreement is found between the structures and properties available in these datasets, and the ones obtained with DFTB.

Microscopic description of fission in superheavy nuclei with the parametrization D1M$$^{*}$$ of the Gogny energy density functional

The constrained Hartree-Fock-Bogoliubov approximation, based on the recent parametrization D1M$^{*}$ of the Gogny energy density functional, is used to describe fission in 435 superheavy nuclei. The Gogny-D1M$^{*}$ parametrization is benchmarked against available experimental data on inner and second barrier heights, excitation energies of the fission isomers and half-lives in a selected set of Pu, Cm, Cf, Fm, No, Rf, Sg, Hs and Fl nuclei. Results are also compared with those obtained with the Gogny-D1M energy density functional. A detailed study of the minimal energy fission paths is carried out for isotopic chains with atomic numbers 100 $\le$ Z $\le$ 126 including very neutron-rich sectors up to around 4 MeV from the two-neutron driplines. Single-particle energies, ground state deformations, pairing correlations, two-nucleon separation energies and barrier heights are also discussed. In addition to fission paths, the constrained Hartree-Fock-Bogoliubov framework provides collective masses and zero-point quantum rotational and vibrational energies. Those quantities are building blocks within the Wentzel-Kramer-Brillouin formalism employed to evaluate the systematic of the spontaneous fission half-lives t$_\mathrm{SF}$. The competition between spontaneous fission and $\alpha$-decay is studied, through the computation of the $\alpha$-decay half-lives t$_\mathrm{\alpha}$ using a parametrization of the Viola-Seaborg formula. From the comparison with the available experimental data and the results obtained with other theoretical approaches, it is concluded that D1M$^{*}$ represents a reasonable starting point to describe fission in heavy and superheavy nuclei.