Calculated Ionization Potentials Research Articles

Polarizable Continuum Models and Green's Function GW Formalism: On the Dynamics of the Solvent Electrons.

The many-body GW formalism, for the calculation of ionization potentials or electronic affinities, relies on the frequency-dependent dielectric function built from the electronic degrees of freedom. Considering the case of water as a solvent treated within the polarizable continuum model, we explore the impact of restricting the full frequency-dependence of the solvent electronic dielectric response to a frequency-independent (ϵ∞) optical dielectric constant. For solutes presenting small to large highest-occupied to lowest-unoccupied molecular orbital energy gaps, we show that such a restriction induces errors no larger than a few percent on the energy level shifts from the gas to the solvated phase. We further introduce a remarkably accurate single-pole model for mimicking the effect of the full frequency dependence of the water dielectric function in the visible-UV range. This allows a fully dynamical embedded GW calculation with the only knowledge of the cavity reaction field calculated for the ϵ∞ optical dielectric constant.

The Astrochemistry Low-energy Electron Cross-Section (ALeCS) database

Context. Electron–molecule interaction is a fundamental process in radiation-driven chemistry in space, from the interstellar medium to comets. Therefore, knowledge of interaction cross sections is key. There have been a plethora of both theoretical and experimental studies of total ionization cross sections spanning from diatomics to complex organics. However, the data are often spread over many sources or are not public or readily available. Aims. We introduce the Astrochemistry Low-energy Electron cross-section (ALeCS) database. This is a public database for electron interaction cross sections and ionization rates for molecules of astrochemical interest. In particular, we present here the first data release, comprising total ionization cross sections and ionization rates for over 200 neutral molecules. Methods. We include optimized geometries and molecular orbital energies at various levels of quantum chemistry theory. Furthermore, for a subset of the molecules, we have calculated ionization potentials. We computed the total ionization cross sections using the binary-encounter Bethe model and screening-corrected additivity rule, and we computed ionization rates and reaction network coefficients for molecular cloud environments. Results. We present the cross sections and reaction rates for >200 neutral molecules ranging from diatomics to complex organics, with the largest being C14H10. We find that the screening-corrected additivity rule cross sections generally significantly overestimate experimental total ionization cross sections. We demonstrate that our binary-encounter Bethe cross sections agree well with experimental data. We show that the ionization rates scale roughly linearly with the number of constituent atoms in the molecule. Conclusions. We introduce and describe the public ALeCS database. For the initial release, we include total ionization cross sections for >200 neutral molecules and several cations and anions calculated with different levels of quantum chemistry theory, the chemical reaction rates for the ionization, and network files in the formats of the two most popular astrochemical networks: the Kinetic Database for Astrochemistry, and UMIST. The database will be continuously updated for more molecules and interactions.

Stability of [10-12]cycloparaphenylene complexes with pristine fullerenes C76,78,84 and endohedral metallofullerenes M3N@C78,80.

[n]Cycloparaphenylenes ([n]CPPs) are strained macrocycles, comprising only sp2-hybridized carbon atoms. In recent years, [n]CPPs have become of great research interest in the field of supramolecular chemistry since their special structure enables the formation of novel host-guest complexes. In this work, we investigate the gas-phase chemistry of noncovalent complexes of [10-12]CPP with the pristine fullerenes C76/78/84 and the endohedral metallofullerenes (EMFs) Sc3N@D3h-C78, Sc3N@D5h-C80 and M3N@Ih-C80 (M = Sc, Y, Lu, Gd). The [1 : 1] complexes with [10-12]CPP are detected as radical cations. The stability and charge distributions of these complexes are studied using energy-resolved collision-induced dissociation (ER-CID). Our results assess the size complementarity, the influence of fullerene symmetry and size as well as the role of the metal size inside the EMF on the binding affinity and complex stability. Two main trends in complex stability have been found: First, [10-12]CPP form more stable complexes with EMFs than with pristine fullerenes and second, all complexes of EMFs with the C80 skeleton show similar stability despite the different metal clusters encapsulated. Another major finding is the fact that [11]CPP is generally the most suitable host for fullerenes with a C76/78/80/84 skeleton. Considering the charge distributions, we observe the existence of two different fragmentation channels for complexes with EMFs where the radical cation is either located at the CPP or at the EMF: (1) [n]CPP+˙ + EMF and (2) [n]CPP + EMF+˙. This behavior allows a clear distinction of the cage isomers ([11]CPP⊃Sc3N@Ih-C80)+˙ and ([11]CPP⊃Sc3N@D5h-C80)+˙ in the MS2 experiment. The experimental results are accompanied by density functional theory (DFT) calculations of ionization potentials (IPs) and fragmentation energies. The computational results fully confirm the measured order of complex stabilities and explain the prevalence of EMF or CPP signals in the spectra by the trend in ionization potentials.

Transition Moments for STEOM-CCSD with Core Triples.

Similarity-transformed equation-of-motion coupled-cluster theory (STEOM-CC) is an alternative approach to equation-of-motion coupled-cluster theory for excited states (EOMEE-CC), which uses a second similarity transformation of the Hamiltonian, followed by diagonalization in a small (CI singles-like) excitation space, even when single and double excitations are included in the transformation. In addition to vertical excitation energies, transition moments measure the strength of the interactions between states determining absorption, emission, and other processes. In STEOM-CCSD, transition moments are calculated in a straightforward manner as biorthogonal expectation values using both the left- and right-hand solutions, with the main difference from EOMEE-CC being the inclusion of the transformation operator. We recently developed an extension of STEOM-CCSD to core excitations, CVS-STEOM-CCSD+cT, which includes triple excitations and the well-known core-valence separation for the core ionization potential calculations. In this work, we derived transition moments for core-excited states with core triple excitations, including both ground-to-core-excited and valence-to-core-excited transitions. The improvement of the computed transition moments of the CVS-STEOM-CCSD+cT method is compared to standard CVS-STEOMEE-CCSD and CVS-EOMEE-CCSD for our previously published small-molecule benchmark set.

Evaluation of Free Radical Quenching Ability of Quinoline Acids through in vitro and Theoretical Studies

Drugs based antioxidants are commonly suggested as targets while designing new medicines. All sorts of pharmaceutical drug development benefit from the extremely desirable quinoline moiety with antioxidant. In this work, the scavenging behaviour of four quinoline derivatives (Q1-Q4) towards DPPH, H2O2, ABTS and superoxide activity were investigated. According to the in vitro inhibition concentration (IC50), quinoline derivative Q1 showed high antioxidant potential. Additionally, the theoretical DFT gas phase calculations of HOMO-LUMO, MEP, NPA and NBO are used to study the conjugating systems in radicals and showed that the N-H site acts more favourable than the O-H site for the radical attack. The calculated bond dissociation energy (BDE) values demonstrated that compound Q1 follows the HAT mechanism and while the calculated ionization potential (IP) and proton dissociation energy (PDE) values showed that Q4 follows the SET-PT route. The results of these two mechanisms demonstrated that radical quenching activity occurs at the N-H and O-H sites. The spin density demonstrates that both radicals are delocalized uniformly across the molecule.

A low-cost four-component relativistic equation of motion coupled cluster method based on frozen natural spinors: Theory, implementation, and benchmark.

We present the theory and the implementation of a low-cost four-component relativistic equation of motion coupled cluster method for ionized states based on frozen natural spinors. A single threshold (natural spinor occupancy) can control the accuracy of the calculated ionization potential values. Frozen natural spinors can significantly reduce the computational cost for valence and core-ionization energies with systematically controllable accuracy. The convergence of the ionization potential values with respect to the natural spinor occupancy threshold becomes slower with the increase in basis set dimension. However, the use of a natural spinor threshold of 10-5 and 10-6 gives excellent agreement with experimental results for valence and core ionization energies, respectively.

Renormalized Singles with Correlation in GW Green's Function Theory for Accurate Quasiparticle Energies.

We apply the renormalized singles with the correlation (RSc) Green function in the GW approximation for accurate quasiparticle (QP) energies and orbitals. The RSc Green function includes singles contributions from the associated density functional approximation (DFA) and considers correlation contributions perturbatively. GRScWRSc uses the RSc Green function as the new starting point and in the formulation of the screened interaction. GRScW0 fixes the screened interaction at the DFA level. For the calculations of ionization potentials, GRScWRSc and GRScW0 significantly reduce the starting point dependence and provide accurate results with errors around 0.2 eV. For the calculations of core-level binding energies, GRScWRSc slightly overestimates the results because of underscreening, but GRScW0 with GGA functionals provides the optimal accuracy with errors of 0.40 eV. We also show that GRScWRSc predicts accurate dipole moments. GRScWRSc and GRScW0, are computationally favorable compared with any self-consistent GW methods. The RSc approach is promising for making GW and other Green function methods efficient and robust.

Investigation of Ionization Potential in Quantum Dots Using the Stratified Stochastic Enumeration of Molecular Orbitals Method.

The overarching goal of this work is to investigate the size-dependent characteristics of the ionization potential of PbS and CdS quantum dots. The ionization potentials of quantum dots provide critical information about the energies of occupied states, which can then be used to quantify the electron-removal characteristics of quantum dots. The energy of the highest-occupied molecular orbital is used to understand electron-transfer processes when invesigating the energy-level alignment between quantum dots and electron-accepting ligands. Ionization potential is also important for investigating and interpreting electron-detachment processes induced by light (photoelectron spectra), external voltage (chemiresistance), and collision with other electrons (impact ionization). Accurate first-principles calculations of ionization potential continue to be challenging because of the computational cost associated with the construction of the frequency-dependent self-energy operator and the numerical solution of the associated Dyson equation. The computational cost becomes prohibitive as the system size increases because of the large number of 2particle-1hole (2p1h) and 1particle-2hole (1p2h) terms needed for the calculation. In this work, we present the Stratified Stochastic Enumeration of Molecular Orbitals (SSE-MO) method for efficient construction of the self-energy operator. The SSE-MO method is a real-space method and the central strategy of this method is to use stochastically enumerated sampling of molecular orbitals and molecular-orbital indices for the construction of the 2p1h and 1p2h terms. This is achieved by first constructing a composite MO-index Cartesian coordinate space followed by transformation of the frequency-dependent self-energy operator to this composite space. The evaluation of both the real and imaginary components of the self-energy operator is performed using a stratified Monte Carlo technique. The SSE-MO method was used to calculate the ionization potentials and the frequency-dependent spectral functions for a series of PbS and CdS quantum dots by solving the Dyson equation using both single-shot and iterative procedures. The ionization potentials for both PbS and CdS quantum dots were found to decrease with increasing dot size. Analysis of the frequency-dependent spectral functions revealed that for PbS quantum dots the intermediate dot size exhibited a longer relative lifetime whereas in CdS the smallest dot size had the longest relative lifetime. The results from these calculations demonstrate the efficacy of the SSE-MO method for calculating accurate ionization potentials and spectral functions of chemical systems.

Real-time equation-of-motion CC cumulant and CC Green's function simulations of photoemission spectra of water and water dimer.

Newly developed coupled-cluster (CC) methods enable simulations of ionization potentials and spectral functions of molecular systems in a wide range of energy scales ranging from core-binding to valence. This paper discusses the results obtained with the real-time equation-of-motion CC cumulant (RT-EOM-CC) approach and CC Green's function (CCGF) approaches in applications to the water and water dimer molecules. We compare the ionization potentials obtained with these methods for the valence region with the results obtained with the coupled-cluster with singles, doubles, and perturbative triples formulation as a difference of energies for N and N - 1 electron systems. All methods show good agreement with each other. They also agree well with the experiment with errors usually below 0.1eV for the ionization potentials. We also analyze unique features of the spectral functions, associated with the position of satellite peaks, obtained with the RT-EOM-CC and CCGF methods employing single and double excitations, as a function of the monomer OH bond length and the proton transfer coordinate in the dimer. Finally, we analyze the impact of the basis set effects on the quality of calculated ionization potentials and find that the basis set effects are less pronounced for the augmented-type sets.

Theoretical analysis and comparison of unitary coupled-cluster and algebraic-diagrammatic construction methods for ionization.

This article describes a novel approach for the calculation of ionization potentials (IPs), or, more generally, electron-detachment energies, based on a unitary coupled-cluster (UCC) parameterization of the ground-state wave function. Explicit working equations for a scheme referred to as IP-UCC3 are given, providing electron-detachment energies and spectroscopic amplitudes of electron-detached states dominated by one-hole excitations correct through third order. In the derivation, an expansion of the UCC transformed Hamiltonian involving Bernoulli numbers as expansion coefficients is employed. Both the secular matrix and the effective transition moments are shown to be essentially equivalent to the strict third-order algebraic-diagrammatic construction scheme for the electron propagator (IP-ADC). Interestingly, due to the Bernoulli expansion, neglecting triple substitutions in the UCC expansion manifold does not affect the third-order consistency of the IP-UCC effective transition moments. Finally, the equivalence between ADC and UCC excited-state schemes is shown to not hold in fourth or higher order due to a different treatment of the correlated excited-state basis.

Taking Advantage of a Systematic Energy Non-linearity Error in Density Functional Theory for the Calculation of Electronic Energy Levels.

We present an approximate approach for the calculation of ionization potential (IP) and electron affinity (EA) by exploiting the complementary energy non-linearity errors for a species M and its one-electron-ionized counterpart (M+). Reasonable IPs and EAs are thus obtained by averaging the orbital energies of M and M+, even with a low-level method such as BLYP/6-31G(d). By combining the corrected IPs and EAs, we can further obtain reasonable excitation energies. The errors in uncorrected valence IPs and uncorrected virtual-orbital energies show systematic trends. These characteristics provide a convenient and computationally efficient avenue for qualitative estimation of these properties with single corrections for multiple IPs and excitation energies.

A DFT investigation of lithium adsorption on graphenes as a potential anode material in lithium-ion batteries

We present a detailed study of the Li+ ion adsorption on two different hydrogenated carbon nanostructures, namely as pristine graphene (PG) and topologic Stone-Wales defective graphene (SWG) using the density functional theory (DFT). The studies are focused to analyze the structure-stability relationship with the estimated electronic and electrical properties for lithium-ion batteries (LIB) formed with an anode based on the Li/Li+#PG and Li/Li+#SWG systems. In addition, the electronic effects induced due to Li+ adsorption and the presence of SW defect on the graphene models were analyzed by the frontier molecular orbitals, ChelpG charges, Raman and UV–Vis spectra. It was verified that Li+ is more stably adsorbed on the edges on both graphene structures through an electrostatic interaction between cation and more negatively charged edges of nanostructures. TD-DFT calculations showed that the metallic nature of isolated graphene is disturbed after the adsorption of Li+, and this was demonstrated from the calculated HOMO-LUMO gap. The same Li+-Graphene geometries were optimized by introducing neutral charge in order to enable the calculation of ionization potentials. I was also found that such systems potentially contributed to the modeling of graphene-based anodes with reasonable electrical voltage responses estimated for a LIB. The simulation of Raman and UV–Vis spectra revealed significant variations in intensity and shifts the typical bands of graphene due to the presence of the Li+ ion that can contribute to point out new experiments to the spectroscopic characterization of these systems. Our results suggest that these carbon nanostructures are potential candidates for efficient applications in electrochemical systems, mainly dealing with LIB.

Electronic Structure of Molecules, Surfaces, and Molecules on Surfaces with the Local Modified Becke-Johnson Exchange-Correlation Potential.

The knowledge of electronic properties of matter is the key to the understanding of its properties and to propose useful applications. To model hybrid organic/inorganic systems with the plane-wave approach, large supercells with many atoms are usually necessary to minimize artificial interactions between periodic images. For such systems, accurate approximations to the exchange-correlation functional of density functional theory, such as hybrid functionals, become computationally expensive, and cheaper approaches need to be considered. Here, we apply the local modified Becke-Johnson exchange-correlation potential to free molecules and surfaces and study its accuracy for calculated ionization potentials. This quantity being important to understand the band alignment of composite heterogeneous systems, we demonstrate the application of the potential to the electronic structure calculation of an exemplary composite semiconductor/molecule system, namely, a F6-TCNNQ molecule adsorbed on a hydrogenated Si(111) surface.

Synthesis, spectroscopic (FT-IR, UV–visible) study, and HOMO-LUMO analysis of adenosine triphosphate (ATP) doped trivalent terbium

The lanthanides and nucleotides can form attractive organic coordination polymers. The ligand complex adenosine-5′-triphosphate (ATP) with metal Terbium (Tb3+) has been successfully synthesized. The complexes were characterized by FT-IR spectroscopy and UV–vis spectroscopy. The results showed that the metal Tb(III) coordinates with adenosine-5′-triphosphate (ATP) through the electrons in the oxygen atom from the phosphate group and the electrons on the nitrogen atom in the adenine ring. FT-IR proved the existence of ATP-Tb with a vibration band of 908 cm−1 and 349 cm−1 to form a P-O-Tb bond and a vibration band of 1635 cm−1 showing the coordination of Nitrogen N1 and N7 atoms as electron donors in terbium metal. The absorption bands at λ = 318.5 nm and 485.5 nm represent the electronic transitions of 7F6 → 5H7 and 7F5 → 5D4 and the redshift occurs after the addition of Tb3+ to ATP with the mole ratio of ATP: Tb [1: 2]. The direct band gap obtained from 4.19 to 4.7 eV as a wide band gap semiconductor material and the indirect band gap obtained from the 5.5–6.0 eV range is an insulator. The HOMO-LUMO energy band gap of the ATP-Tb complex is 3.721 eV. This value is similar to that obtained from experiments using the UV–visible spectrum. Calculations of band gap energies, interactions, and spectral properties of complex compounds can provide the basis for the design of wide band gap semiconductor materials for rare earth complexes with organic ligands. The electronic properties of ATP-Tb have been calculated Ionization potential (I), electron affinity (A), chemical hardness (η), chemical softness (ζ), chemical potential (μ), electronegativity (Х), dan electrophilicity index (ω).

In Silico Investigation of Electronic Structure, Binding Patterns and Molecular Docking of Nevirapine: An anti-HIV Type-1 Drug

Nevirapine is used in the treatment of Human Immunodeficiency Virus Type 1 (HIV-1) infection. The structure of nevirapine belongs to the dipyridodiazepinone class of chemical. In the present work, molecular geometries of nevirapine drug, AU and GC base pairs have been optimized by DFT method with B3LYP/6-31G(d,p) basis set. The MEP and HOMO-LUMO surfaces have been scanned at 0.001 electron/Bohr3 isodensity surface. Further, HOMO-LUMO energies have been used to calculate ionization potential, electron affinity, electronegativity, global hardness and softness parameters of the drug molecule as well as AU and GC base pairs. IR and Raman spectra of the drug molecule have been analyzed in the light of standard data. Results obtained from NBO analysis have been analyzed in terms of the hybridization of atoms and electronic structure of drug molecule. Binding patterns of the drug molecule with nucleic acid base pairs (AU and GC) have been examined using second order perturbation theory valid at intermediate range. Efforts have been made to elucidate the chemical and biological properties of the drug. The inhibition activity of the drug molecule against HIV-1 reverse transcriptase (Y2NG) in complex with inhibitor GSK560 has been examined with the help of molecular docking. It has been observed that nevirapine prefers to bind in the guanine-cytosine rich region of nucleic acid helices. Further, there exists gross similarity between calculated vibrational assignment and the standard data as reported in the literature.

Predicting Properties of Iron(III) TAML Activators of Peroxides from Their III/IV and IV/V Reduction Potentials or a Lost Battle to Peroxidase.

A cyclic voltammetry study of a series of iron(III) TAML activators of peroxides of several generations in acetonitrile as solvent reveals reversible or quasireversible FeIII/IV and FeIV/V anodic transitions, the formal reduction potentials (E°') for which are observed in the ranges 0.4-1.2 and 1.4-1.6 V, respectively, versus Ag/AgCl. The slope of 0.33 for a linear E°'(IV/V) against E°'(III/IV) plot suggests that the TAML ligand system plays a bigger role in the FeIII/IV transition, whereas the second electron transfer is to a larger extent an iron-centered phenomenon. The reduction potentials appear to be a convenient tool for analysis of various properties of iron TAML activators in terms of linear free energy relationships (LFERs). The values of E°'(III/IV) and E°'(IV V-1 ) correlate 1) with the pKa values of the axial aqua ligand of iron(III) TAMLs with slopes of 0.28 and 0.06 V, respectively; 2) with the Stern-Volmer constants KSV for the quenching of fluorescence of propranolol, a micropollutant of broad concern; 3) with the calculated ionization potentials of FeIII and FeIV TAMLs; and 4) with rate constants kI and kII for the oxidation of the resting iron(III) TAML state by H2 O2 and reactions of the active forms of TAMLs formed with donors of electrons S, respectively. Interestingly, slopes of log kII versus E°'(III/IV) plots are lower for fast-to-oxidize S than for slow-to-oxidize S. The log kI versus E°'(III/IV) plot suggests that the manmade TAML catalyst can never be as reactive toward H2 O2 as a horseradish peroxidase enzyme.

Synthesis of 1-aroyl-3-methylsulfanyl-5-amino-1,2,4-triazoles and their analysis by spectroscopy, X-ray crystallography and theoretical calculations

N-Aroyl-1,2,4-triazoles TAM and TACl were regioselectively synthesized in excellent yields through an efficient N-acylation reaction of 3-amino-5-methylsulfanyl-1H-1,2,4-triazole with aroyl chlorides. Structures of N-aroyl-1,2,4-triazoles were studied by single-crystal X-ray diffraction, observing that their crystal structures are characterized by the formation of dimers through N‒H‧‧‧N bonds. The supramolecular assembly depends on the sort of connections between dimers, which notably change with the para-substituent on the aroyl group. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (χ), electrophilicity index (ω), hardness (η), and chemical potential (μ) are correlated with the HOMO and LUMO orbital energies. Moreover, molecular electrostatic potential maps of both molecules have been calculated showing a negative region at N2 atom of the 1,2,4-triazole ring instead of exocyclic amino group. The vibrational spectral analysis was carried out using infrared spectroscopy in the range 4000–400 cm−1 for N-aroyl-1,2,4-triazoles TAM and TACl. The experimental spectra were recorded in the solid state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6–31G(d,p) method and basis set yielding fairly good agreement between observed and calculated frequencies. Simulation of infrared spectra utilizing the results of these calculations led to an excellent overall agreement with the observed spectral patterns.

Photophysical properties and theoretical photosensitization mechanism of non-peripherally dodecyloxy substituted metallophthalocyanines for photodynamic therapy

Non-peripherally tetradodecyloxy substituted copper (CuPc 3) and nickel (NiPc 4) phthalocyanines and the compounds were synthesized. The absorption spectra of synthesized Pcs were showed monomeric behavior evidenced by a narrow between 680 and 750 nm (Q band) for CuPc(3) and NiPc(4) in different solvents. The fluorescence behavior of the Pcs was studied in chloroform. The CuPc (3) showed outstanding stability in THF as solvent during photodegradation studies. The possible photodynamic therapy reaction mechanisms were studied through the calculation of ionization potentials and electron affinity in both vacuum and solvents using SCRF model.

From simple molecules to nanotubes. Reliable predictions of ionization potentials from the ΔMP2-SCS methods

The vertical ionization potentials for systems of various sizes, ranging from simple molecules, DNA/RNA bases, donor and acceptor organic molecular systems as well as nanotubes are calculated using the ΔMP2-SCS family of methods [Śmiga et al 2018 J. Chem. Theory Comput. 14 4780–90]. We have shown that for all investigated cases, the ΔMP2-SCS methods, being almost cost free single-step post-Hartree–Fock calculation, provide very accurate vertical ionization potentials comparable in quality with state-of-art outer valence Green’s function methods. Moreover, we show that a combination of the ΔMP2-SCS methods with the resolution of identity technique is effective and reliable an alternative to the semi-empirical density functional theory methods and Green’s function-based calculations of ionization potentials for large molecular systems such as silicon-based or organic-based solar cells, for which the IP-EOM-CCSD calculations are too expensive for routine calculations.

Calculated Ionization Potentials of MO3 and MO2 for M = U, Mo, W, and Nd

Ionization potentials (IPs) for MO3 and MO2 for M = U, Mo, W, and Nd have been predicted using the Feller-Peterson-Dixon (FPD) approach at the coupled cluster CCSD(T)/complete basis set level including additional corrections. The additional corrections are mostly small, with spin-orbit effects contributing less than 0.05 eV, except for NdO2 where the correction lowers the IP by 0.26 eV. The IPs for UO3 and UO2 are calculated to be 9.59 and 6.09 eV, respectively. The calculated IPs for MoO3 and WO3 are very similar, 11.13 and 11.11 eV, respectively, and MoO2 and WO2 are 8.51 and 8.79 eV, respectively. MoO2 has a triplet ground state, whereas WO2 has a singlet ground state. The calculated IP for NdO2 is 7.90 eV. NdO3 does not achieve a high +VI formal oxidation state on the lanthanide and has an IP of 7.80 eV. These calculated IPs are expected to have error bars of ±0.04 eV.