Calculated Electron Affinities Research Articles

Systematic construction of complementary auxiliary basis sets from and for atomic natural orbitals

A systematic way to construct compact complementary auxiliary basis sets (ABSs) from and for atomic natural orbital basis sets for the use as resolution-of-the-identity sets in explicitly correlated F12 calculations is presented. The performance of these newly constructed ABSs has been benchmarked in explicitly correlated calculations of absolute energies, ionisation potentials and electron affinities.

Understanding and Reducing Errors in Density Functional Calculations

We decompose the energy error of any variational density functional theory calculation into a contribution due to the approximate functional and that due to the approximate density. Typically, the functional error dominates, but in many interesting situations the density-driven error dominates. Examples range from calculations of electron affinities to preferred geometries of ions and radicals in solution. In these abnormal cases, the error in density functional theory can be greatly reduced by using a more accurate density. A small orbital gap often indicates a substantial density-driven error.

Formation of S–Cl Phosphorothioate Adduct Radicals in dsDNA S-Oligomers: Hole Transfer to Guanine vs Disulfide Anion Radical Formation

In phosphorothioate-containing dsDNA oligomers (S-oligomers), one of the two nonbridging oxygen atoms in the phosphate moiety of the sugar-phosphate backbone is replaced by sulfur. In this work, electron spin resonance (ESR) studies of one-electron oxidation of several S-oligomers by Cl2(•-) at low temperatures are performed. Electrophilic addition of Cl2(•-) to phosphorothioate with elimination of Cl(-) leads to the formation of a two-center three-electron σ(2)σ*(1)-bonded adduct radical (-P-S-̇Cl). In AT S-oligomers with multiple phosphorothioates, i.e., d[ATATAsTsAsT]2, -P-S-̇Cl reacts with a neighboring phosphorothioate to form the σ(2)σ*(1)-bonded disulfide anion radical ([-P-S-̇S-P-](-)). With AT S-oligomers with a single phosphorothioate, i.e., d[ATTTAsAAT]2, reduced levels of conversion of -P-S-̇Cl to [-P-S-̇S-P-](-) are found. For guanine-containing S-oligomers containing one phosphorothioate, -P-S-̇Cl results in one-electron oxidation of guanine base but not of A, C, or T, thereby leading to selective hole transfer to G. The redox potential of -P-S-̇Cl is thus higher than that of G but is lower than those of A, C, and T. Spectral assignments to -P-S-̇Cl and [-P-S-̇S-P-](-) are based on reaction of Cl2(•-) with the model compound diisopropyl phosphorothioate. The results found for d[TGCGsCsGCGCA]2 suggest that [-P-S-̇S-P-](-) undergoes electron transfer to the one-electron-oxidized G, healing the base but producing a cyclic disulfide-bonded backbone with a substantial bond strength (50 kcal/mol). Formation of -P-S-̇Cl and its conversion to [-P-S-̇S-P-](-) are found to be unaffected by O2, and this is supported by the theoretically calculated electron affinities and reduction potentials of [-P-S-S-P-] and O2.

How to Find Out Whether a 5-Substituted Uracil Could Be a Potential DNA Radiosensitizer

Incorporated into genomic DNA, 5-substituted uracils could be employed in human cancer radiotherapy if they could be sensitized to dissociate upon reaction with hydrated electrons. Using the B3LYP/6-31++G(d,p) method, we calculate electron affinities and energy profiles related to the dissociation of the respective anions for a series of uracil derivatives. We demonstrate that for a uracil analogue to be an efficient electron acceptor the uracil substituent has to possess significant electron-withdrawing power. On the other hand, in order to ensure effective dissociation of the anion, the chemical bond holding together the substituent and uracil residue should be relatively weak. Our theoretical predictions are in excellent agreement with the results of our negative ion photoelectron spectroscopy experiments. We propose two new potential sensitizers that seem to possess the required properties, although they have never been tested in radiobiological experiments.

Ab initio study and spectral simulation of the [formula omitted] photodetachment processe of dichlorocarbene anion

Combining ab initio molecular orbital calculations with Franck–Condon analysis to simulate vibrationally resolved photoelectron spectra have been carried out on the CCl2(X̃1A1)←CCl2-(X̃2B1) detachment process. By using CCSD/6-311+G(2d, p) values, the theoretical spectra obtained are in agreement with the observed one, and, the equilibrium geometry parameters, 1.890±0.002Å and 102.9±0.3° of the X̃2B1 state of CCl2− are acquired, by employing an iterative Franck–Condon (IF–C) analysis procedure. In addition, on different levels of theory, our best calculated electron affinity (EA) is in fair agreement with the experimental value.

Density Functional Theory Calculations of the Redox Potentials of Actinide(VI)/Actinide(V) Couple in Water

The measured redox potential of an actinide at an electrode surface involves the transfer of a single electron from the electrode surface on to the actinide center. Before electron transfer takes place, the complexing ligands and molecules of solvation need to become structurally arranged such that the electron transfer is at its most favorable. Following the electron transfer, there is further rearrangement to obtain the minimum energy structure for the reduced state. As such, there are three parts to the total energy cycle required to take the complex from its ground state oxidized form to its ground state reduced form. The first part of the energy comes from the structural rearrangement and solvation energies of the actinide species before the electron transfer or charge transfer process; the second part, the energy of the electron transfer; the third part, the energy required to reorganize the ligands and molecules of solvation around the reduced species. The time resolution of electrochemical techniques such as cyclic voltammetry is inadequate to determine to what extent bond and solvation rearrangement occurs before or after electron transfer; only for a couple to be classed as reversible is it fast in terms of the experimental time. Consequently, the partitioning of the energy theoretically is of importance to obtain good experimental agreement. Here we investigate the magnitude of the instantaneous charge transfer through calculating the fast one electron reduction energies of AnO2(H2O)n(2+), where An = U, Np, and Pu, for n = 4-6, in solution without inclusion of the structural optimization energy of the reduced form. These calculations have been performed using a number of DFT functionals, including the recently developed functionals of Zhao and Truhlar. The results obtained for calculated electron affinities in the aqueous phase for the AnO2(H2O)5(2+/+) couples are within 0.04 V of accepted experimental redox potentials, nearly an order of magnitude improvement on previous calculated standard potentials E(0) values, obtained using both DFT and high level multireference approaches.

GWcalculations using the spectral decomposition of the dielectric matrix: Verification, validation, and comparison of methods

In a recent paper [Nguyen et al., Phys. Rev. B 85, 081101(R) (2012)] we presented an approach to evaluate quasiparticle energies based on the spectral decomposition of the static dielectric matrix. This method does not require the calculation of unoccupied electronic states or the direct diagonalization of large dielectric matrices, and it avoids the use of plasmon-pole models. The numerical accuracy of the approach is controlled by a single parameter, i.e., the number of eigenvectors used in the spectral decomposition of the dielectric matrix. Here we present a comprehensive validation of the method, encompassing calculations of ionization potentials and electron affinities of various molecules and of band gaps for several crystalline and disordered semiconductors. We demonstrate the efficiency of our approach by carrying out $GW$ calculations for systems with several hundred valence electrons.

Theoretical Studies on the Electronic Structures and Spectral Properties of Three Iridium(III) Complexes With Different NˆN Ligands

We report a quantum chemical study of the electronic structures and spectral properties of three iridium(III) biscarbene complexes with different heteroleptic N^N ligands. The theoretical calculation reveals that the lowest-lying singlet absorptions at 434 nm for 1 and 487 nm for 3 are attributed to the mixed transition characters of metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT). However, for 2, the lowest-lying singlet absorption at 509 nm is attributed to the MLCT. For 1–3, the phosphorescence at 739, 913, and 737 nm are mainly attributed to 3MLCT and 3LLCT characters. For 1 and 3, the emission energies are nearly the same, which is larger than that of 2. Ionization potentials (IP) and electron affinities (EA) calculations show that the assumed complex 3 has large EA value and enhanced electron injection ability as compared to complexes 1 and 2. Moreover, the reasons for different transition characters and phosphorescence quantum yield for the three complexes have been discussed in this paper. This theoretical contribution allows the factors determining the efficiency of radiative and nonradiative decay pathways in the three complexes.

DFT study of gadolinium aluminohydrides and aluminofluorides

First-principles calculations using density functional theory were performed to study the structure, stability and electronic properties of clusters formed by attaching AlH4 and AlF4 complexes to the Gd atom. The calculated electron affinity of AlH4 is 3.58eV, close to that of chlorine, and for the Gd (AlH4)4 cluster it is 4.95eV, indicative of superhalogen behavior. For AlF4 the calculated electron affinity is 7.36eV, indicating superhalogen behavior. When this complex is used to decorate Gd in number that exceeds its formal valence (+3) the electron affinity increases to 8.42eV in the Gd (AlF4) 4 cluster, which is an indication of hyperhalogen behavior. High-spin ground states are predicted for these moieties, which have same spin multiplicities in both aluminohydrides and aluminofluorides.

Ab initio and anion photoelectron studies of Rhn (n = 1 − 9) clusters

Anion photoelectron spectroscopy (PES) and ab initio calculations have been used to identify the unique structural, electronic, and magnetic properties of both neutral and anionic Rh n (n = 1 − 9) free standing clusters. Negative ion photoelectron spectra are presented for electron binding energies up to 3.493 eV. We discuss our computational results in the context of the PES experiment, in which the calculated electron affinities and vertical detachment energies are in good agreement with the measured values. Theoretically, we investigate the low-lying energy structures and the spin isomers of each neutral and anionic rhodium cluster and infer their magnetic moments. Our results show that octahedral and tetrahedral motifs are favoured in contrast to cubic motifs. Both experimental and theoretical results obtained here are compared and discussed with previous experimental and theoretical studies on the same systems.

Reactions of excess electrons with “bridged” amidoesters in low-temperature matrices

Structure of radical anions of “bridged” amidoesters MeOOC(CH2)nCONMe2 (n=0–3) generated by X-ray irradiation was investigated by EPR, optical absorption spectroscopy and quantum-chemical calculations. Amidoester-0 (n=0) has positive calculated electron affinity and the corresponding delocalized radical anion is stabilized independent of matrix polarity. Meanwhile, for amidoesters with n=1–3 groups possessing apparently negative intrinsic electron affinity the role of matrix in stabilization of the corresponding radical anions becomes crucial. Two types of the localized radical anions were observed in the latter case.

Ab initio calculation of ionization potential and electron affinity of six common explosive compounds

Ab initio calculation of ionization potential and electron affinity of six common explosive compounds Jason K Cooper,1 Christian D Grant,2 Jin Z Zhang11Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA, 2Physical and Life Sciences, Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA, USAAbstract: The vertical and adiabatic ionization potential (IPV and IPA) and vertical electron affinity (EAV) for six explosives, hexogen (RDX), octogen (HMX), triacetone triperoxide (TATP), hexamethylene triperoxide diamine (HMTD), 2,4,6-trinitrotoluene (TNT), and pentaerythritol tetranitrate (PETN), have been studied using ab initio computational methods. The IPV was calculated using MP2, CBS-QB3, and Koopmans’ theory, while the IPA was calculated with B3LYP, CAM-B3LYP, ψB97XD, B2PLYP, and MP2 using the ΔE method for the ground state B3LYP optimized geometries. IPAs of RDX and TNT were also calculated using CBS-QB3 with relaxed geometries of the ions. Of the methods tested, B3LYP and B2PLYPD provided superior and more consistent results for calculating the IP compared to CBS-QB3 level IPA calculations and experimental data (where available). CBS-QB3 was used as a benchmark for calculating the EAV as experimental data has not been reported. For calculations of the EAV, B3LYP performed the worst while MP2 and B2PLYPD predicted values closest to those made by CBS-QB3. Basis set effects were evaluated using 6-31+G(d,p), 6-311+G(d,p), and 6-311+G(3df,2p) for both IP and EA. 6-31+G(d,p) gave satisfactory results for calculating IP while 6-311+G(3df,2p) had improved results for calculating the EA. The four nitro-containing compounds have exothermic reduction potentials while the peroxides are endothermic. In addition, it was determined that RDX, HMX, TATP, and HMTD had unstable geometries in their reduced forms. The results should be useful in developing detection and screening methods including ionization methods for mass spectroscopy and fluorescence quenching methods of detection.Keywords: ionization, affinity, explosive, TNT, ab initio, DFT

Determination of Barrier Heights for Proton Exchange in Small Water, Ammonia, and Hydrogen Fluoride Clusters with G4(MP2)-Type, MPn, and SCS-MPn Procedures-A Caveat.

Calculation of accurate water-water interaction energies is of fundamental importance in computational modeling of many biological and chemical phenomena. We have obtained benchmark barrier heights for proton-exchange reactions and complexation energies in water clusters (H2O)n (n = 1-6) by means of the high-level W1-F12 procedure. We find that lower-cost composite procedures (e.g., G4(MP2) and G4(MP2)-6X), as well as MP2 and SCS-MP2, exhibit surprisingly poor performance for the barrier heights of reactions involving multiple proton exchanges. Moreover, the performance significantly deteriorates with increasing size of the clusters. Similar observations apply to complexation energies in water clusters, and to barrier heights for proton exchange in ammonia and hydrogen fluoride clusters. We propose a modified version of G4(MP2)-6X (denoted G4(MP2)-6X+) that includes sp- and d-diffuse functions in the CCSD(T) term, which gives excellent proton-exchange barrier heights at a computational cost only slightly greater than that of standard G4(MP2). G4(MP2)-6X+ also leads to a substantial improvement over G4(MP2) and G4(MP2)-6X for the calculation of electron affinities.

Franck–Condon analysis of the photoelectron spectra of HCCl−: Considering Duschinsky effects

Franck–Condon analysis and spectral simulations were carried out on the HCCl (X˜1A′)←HCCl-(X˜2A″) photo-detachment process. The theoretical spectra obtained by using CCSD/6-311+G(2p,d) values are in agreement with the observed one. Otherwise, the equilibrium geometry parameters, r(CCl)=1.950±0.002Å of the X˜2A″ state of HCCl− are derived, by using the spectral simulation and employing an iterative Franck–Condon (IF–C) analysis procedure. Furthermore, through the different methods, our best calculated electron affinity is 1.2106eV, which is in fair agreement with the experimental value.

Theoretical study for the electron affinities of negative ions with the MCDHF method

Systematic theoretical calculations based on the multi-configuration Dirac–Hartree–Fock method have been carried out for the electron affinities of anions of the elements of group III (B, Al, Ga, In and Tl), group IV (C, Si, Ge, Sn and Pb), group V (N, P and As), group VI (O, S, Se, Te and Po) and group VII (F, Cl, Br, I and At) by studying the ground energies of neutral atoms and their corresponding negative ions. The differences between the calculated total energies of the neutral atom and its anion were used to obtain the electron affinities. We discuss in detail the effects of configuration interaction, investigate the importance of including different types of correlations and check the impact of the higher order relativistic corrections on electron affinities. Our calculated electron affinities are compared with experimental and other available theoretical results. The present studies are the first systematic studies of all these elements. We give the first theoretical values for the affinities of elements Se, Te, Po and At; thereinto, there is no experimental value for elements Po and At.

Infinite Basis Set Extrapolation for Double Hybrid Density Functional Theory 2: Effect of Adding Diffuse Basis Functions

AbstractWe applied the Infinite Basis (IB) set extrapolation and Double Hybrid Density Functional Theory (DHDF) to calculate the electron affinities, reaction barrier heights, proton affinities, non‐covalent interactions, atomization, ionization, and alkyl bond dissociation energies. We previously found that the mean unsigned error of the B2KPLYP‐IB calculation with the combination of cc‐pVTZ and cc‐pVQZ reach the chemical accuracy limit (∼2 kcal/mol) where the largest deviation occurred in the electron affinity calculations and the weak interactions between noble gases and nonpolar molecules. Here, we investigated the basis set effect using the B2KPLYP‐IB extrapolation scheme that involves (1) the addition of extra tight d basis functions to the second row elements (i.e. cc‐pV(L+d)Z), (2) the addition of extra s, p, and d diffuse basis functions, and (3) a comparison between Dunning's Correlation Consistent and Jensen's Polarization Consistent (pc‐L) basis sets. We found that the addition of extra s and p diffuse basis functions formed the minimal augmented basis sets proposed by Truhlar. This addition permitted the B2KPLYP‐IB to reach the chemical accuracy limit with the combination of the double ζ and triple ζ basis sets. Adding extra s, p diffuse functions to the pc‐L series permitted only a small improvement. This small improvement is due to the fact that the pc‐L basis sets already contain a large number of functions for the p block elements. Taken together, the results suggest that this minimal augmented basis sets is useful for due to its accuracy and affordable computational cost.

Prediction of Reduction Potentials from Calculated Electron Affinities for Metal-Salen Compounds

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Novel quinonediimines derived from amino acid-like structures 2: Characterization and DFT computational study of N,N′-bis(4′-l-phenylalaninyl)-1,4-quinonediimine

Density functional calculations were performed on N,N′-bis(4′-l-phenylalaninyl)-1,4-quinonediimine, a novel substituted aniline “trimer.” This is the second reported symmetric quinonediimine with outer rings derived from amino-acid related structures, the first of which derived from an unmodified, naturally occurring amino acid. Results of the calculations were compared to experimental properties of the herein synthesized trimer. The calculated HOMO levels for isomers of the title compound range from −6.0423 to −6.0178eV, and the LUMO levels from −3.1794 to −3.1772eV. The calculated electron affinities range from 2.1509 to 2.1554eV. The LUMO level is lowest for the syn isomer, and the electron affinity greatest in magnitude for the anti isomer. Compared to the widely-studied amino-capped aniline trimer N,N′-bis(4′-aminophenyl)-1,4-quinonediimine, the title compound has lower LUMO levels and greater electron affinity in both the emeraldine base or emeraldine dihydrochloride (salt) form, suggesting that it might be even more effective in corrosion control applications. Because the outer rings are derived from amino-acid related structures, such molecules, particularly as capping groups for polyanilines, could find use in biomedical applications.

Computational studies on the injection, transport, absorption, and phosphoresce properties of a series of cationic iridium (III) complexes [Ir(C∧N)2(L)2]+ (C∧N = ppy, tpy, dfppy, bzq)

AbstractQuantum chemistry methods are applied to investigate the electronic structures, injection and transport properties, absorption and phosphorescence mechanism of a series of Iridium (III) complexes [Ir(C∧N)2(L)2]+ (L = 4‐pyCO2Et; C∧N = 2‐phenylpyridine, 1; 2‐(4‐tolyl)pyridine, 2; 2‐(4,6‐difluorophenyl)pyridimato, 3; benzoquinoline, 4), which may be used as emitters on organic light emitting diodes (OLEDs). Calculations of ionization potentials and electron affinities are used to evaluate the injection abilities of holes and electrons into these complexes. The reorganization energy (λ) calculations show that the four complexes are suitable as emitters in OLEDs. The absorptions and emissions can be tuned by adding substituent to the ppy ligand or extending the π‐conjugation effect of the C∧N ligand, and quantum yields of 1–4 are investigated. In addition, no solvent effect is observed in the absorption and emission spectra. © 2012 Wiley Periodicals, Inc.

The effect of local approximations in the ground-state coupled cluster wave function on electron affinities of large molecules

A possibility to calculate electron affinities (EAs) by a software devised for electron excitations is exploited to examine the accuracy of a partly local EA-EOM-CCSD method. In the proposed approach local approximations are applied to the ground-state coupled cluster wave function, while the EAs themselves are obtained in a full configurational space. The results of a numerical test for 14 molecules show that already with standard local settings the method reproduces the nonlocal EAs with the average error of 0.009 eV. Since the EA-EOM step of the calculation requires less computational resources than the computation of the CCSD ground state, the proposed hybrid approach can become a valuable tool for obtaining the EAs for molecules, which are too large for a canonical CCSD calculation, but still small enough for the EA-EOM step to be performed in a nonlocal way.