DFT calculations of the ionization potentials and electron affinities of serinamide

Adiabatic and vertical ionization potentials (IPs) and valence electron affinities (EAs) of serinamide in the gas phase have been determined using density functional theory (DFT) B3LYP, B3P86, and B3PW91 methods with the 6‐311++G** and 6‐311G** basis sets, respectively. IPs and EAs of serinamide in solution have been calculated with the B3LYP method using the 6‐311++G** and 6‐311G** basis sets. Eight possible conformers of serinamide and its charged states in the gas phase have been optimized employing the DFT B3LYP method with 6‐311++G** and 6‐311G** basis sets, respectively. All the adiabatic and vertical ionization potentials (AIPs and VIPs) of eight serinamide conformers in our work are positive values, whether in the gas phase or in solutions; the IPs in solutions are smaller than the results in the gas phase and decrease with increased dielectric constants in solutions. This finding indicates that the cationic states in solutions are more stable than those in the gas phase. All EAs of eight serinamide conformers are negative values in the gas phase, indicating that the anionic states are unstable with respect to electron autodetachment, both adiabatically and vertically. In contrast, all other adiabatic electron affinities (AEAs) are negative values in solutions except for 6S in water; 7S in chloroform, acetone, and water; and 8S in acetone and water, and increase with increasing of dielectric constants in solutions. All vertical electron affinities (VEAs) are negative values in solutions; however, no good rule has been found for these values in solutions. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Theoretical determination of electron affinity and ionization potential of DNA and RNA bases

The ionization potentials and electron affinities of thymine, cytosine, adenine, guanine, and uracil were determined at density functional level using different exchange‐correlation functionals and basis sets. Results showed that the computed ionization potentials are very close to the experimental counterparts. The sign of adiabatic electron affinities of adenine, thymine, and uracil is unaffected by the used level of theory while that for guanine and cytosine depends on both the used potential and basis set. Vertical electron affinities are always negative in agreement with the experimental indications. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1243–1250, 2000     

Density functional study of the structural,electronic, and magnetic properties of neutral and charged rhodium clusters up to tetramer

Model core potential computations were performed for Rh₂, Rh₃, and Rh₄ clusters and their respective cations and anions using the linear combination of Gaussian‐type orbital, nonlocal spin density method. The optimized geometries, electronic and magnetic structures, binding and fragmentation energies, adiabatic ionization potentials, and electron affinities were determined. Results show that the ionization potentials, electron affinities, binding energies, and magnetic moments decrease with the cluster size. For Rh₂ and Rh₃ the most stable structures exhibit ferromagnetic properties, while Rh₄ in its ground state is found to be paramagnetic. The structures of minimum energy for the charged species often differs from the corresponding neutral one. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

DFT Calculations for Electron Transfer Bond-breakingReaction of CH_3-X

Bond-breaking in electron tansfer (ET) reaction is a powerful synthetic tool to provide alkyl radicals. The reaction RX + e( ? R( + X( in gas-phase yields directly the alkyl radical and the halide ion. Although ab initio calculation has been performed to this kind of reaction for CH3-X1-3, density functional theory (DFT) has not been invoked so far. DFT is gaining popularity recently as a cost-effective procedure for studying physical properties of molecules. The activation energy ((G#) …     

金镍二元团簇结构和电子性质的理论研究

在UBP86/LANL2DZ和UBP86/def2-TZVP水平下详细研究了AumNin (m＋n≤6)团簇的几何结构和电子性质. 详细地分析了团簇的结构特征, 平均结合能, 垂直电离势, 垂直电子亲和能, 电荷转移以及成键特征. 所有混合团簇中, 镍原子趋于聚集到一起, 形成最多Ni—Ni键, 金原子分布在镍原子聚集体周围以形成最多Au—Ni键. Ni原子较少团簇的电子性质与纯金团簇类似, 呈现一定奇偶振荡. 混合团簇中存在镍到金原子间的电荷转移. Ni原子较少团簇中, 自旋电子主要定域在Ni原子上, Ni原子较多团簇中, Au原子明显受到自旋极化. 混合团簇的分波态密度表明, AuNi混合团簇对小分子的反应活性要高于纯金团簇.     

DFT,CBS‐Q,W1BD and G4MP2 calculation of the proton and electron affinities,gas phase basicities and ionization energies of saturated and unsaturated carboxylic acids (C1–C4)

The proton affinities, gas phase basicities and ionization energies of formic acid, acetic acid, propanoic acid, 2‐propenoic acid, propiolic acid, butanoic acid, 2‐butenoic acid, 3‐botenoic acid, 2‐methyl‐propanoic acid and 2‐methyl‐2‐propenoic acid were calculated using the computational methods including B3LYP/6‐311++G(2df,p), CBS‐Q and G4MP2. Also, the considered properties were calculated using W1BD method only for formic and acetic acids. In addition, the electron affinities of the acids were calculated using B3LYP, CBS‐Q, G4MP2 and G2MP2 methods, separately. The calculations showed that the PA and gas phase basicity increase with the increase in the number of carbon atoms. The calculated Ionization energies of the unsaturated carboxylic acids are less than the corresponding saturated acids, which are in good agreement with the experimental results. © 2013 Wiley Periodicals, Inc.     

Ionization and protonation of MgC3: A theoretical study

A theoretical study of the MgC₃⁺ and MgC₃H⁺ species has been carried out. Predictions for their geometries and vibrational frequencies have been made at both second‐order Møller–Plesset (MP2) and B3LYP levels, whereas electronic energies have been computed at G2 and coupled cluster single and double excitation model augmented with a noniterative triple excitation conection (CCSD(T)) levels. The predicted global minimum for MgC₃⁺ is a rhombic structure (²A₁ electronic state), whereas a T‐shaped structure and an open‐chain isomer lie about 10 and 12 kcal/mol, respectively, higher in energy. In the case of MgC₃H⁺ the predicted global minimum is also a four‐membered ring obtained upon protonation of the most stable neutral isomer. Low ionization potentials and high proton affinities are generally obtained, especially for the most stable MgC₃⁺ isomer. The estimated values at the CCSD(T) level for the predicted global minimum are 7.20 eV [ionization potential (IP)] and 256.5 kcal/mol [proton affinities (PA)]. Therefore, if present in the interstellar medium, MgC₃ should be easily ionized and would react quite easily to give the protonated species. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Ionisation Potential, Electron Affinity and Polar Bond: A First-order Correction Method for Interaction Energy

A new first-order method is proposed to improve the potential energy of the polar molecules. The nature of the polar bonding is illustrated by some examples, LiF, LiO, LiH, ScO, and AlO molecules, covering from strong to weak ionic cases. A simple first-order correction method using the dipole moment or the effective charge, and the experimental and theoretical ionisation potentials and electron affinities is explained. Application of this method to those molecules improves remarkably the spectroscopic constants. This method can be easily extended to polyatomic cases involving a polar bonding between an electropositive moiety (electron donor) and an electronegative functional group (electron acceptor).     

SinH/SinH-(n=3～8)的结构和电子亲合能的研究

选用四种不同的密度泛函理论方法(B3LYP，B3P86，BLYP，BP86)，在全电子的双ξ加极化加弥散函数基组(DZP )下，对SinH／SinH^-(n=3～8)体系进行研究，获得它们的基态结构和电子亲合能。预测Si3H／Si3H^-,Si4H／Si4H^-,Si5H／Si5H^-,Si6H／Si6H^-，Si7H／Si7H^-和Si8H／Si8H^-的基态结构分别为C2v(^2B2)／C2v(1^A1)氢桥结构，Cs(^2A’)／C(^1A’)，C2v(^2B2)／C2v(^1A1)，C2v(^2B2或^2B1)／C4v(^1A1)，C5v(^2A1)／C5v(^1A1)和C5(^2A‘‘)／C3v(^1A1)。在电子亲合能方面，B3LYP方法预测的电子亲合能是最可靠的，预测Si3H，Si4H，Si5H，Si6H，Si7H和Si8H的电子亲合能分别为2．56，2．59，2．84，2．86，3．19和3．14eV。     

Design of low band gap polymers employing density functional theory—hybrid functionals ameliorate band gap problem

Band gaps in solids and excitation energies in finite systems are underestimated significantly if estimated from differences between eigenvalues obtained within the local spin density approximation (LSDA). In this article we present results on 20 small- and medium-sized π-systems which show that HOMO–LUMO energy differences obtained with the B3LYP, B3P86, and B3PW91 functionals are in good agreement with vertical excitation energies from UV-absorption spectra. The improvement is a result of the use of the exact Hartree–Fock exchange with hybrid methods. Negative HOMO energies and negative LUMO energies do not provide good estimates for IPs and EAs. In contrast to Hartree–Fock theory, where IPs are approximated well and EAs are given poorly, DFT hybrid methods underestimate IPs and EAs by about the same amount. LSDA yields reasonable EAs but poor IPs. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1943–1953, 1997     

Poly(pyrazinoquinoxaline)s: New n‐Type Conjugated Polymers That Exhibit Highly Reversible Reduction and High Electron Affinity

Summary: The pyrazinoquinoxaline‐based conjugated polymers poly(2,7‐diphenylpyrazino(2,3‐g)quinoxaline‐3,8‐diyl‐1,4‐phenylene) (PZQP) and poly(2,7‐diphenylpyrazino(2,3‐g)quinoxaline‐3,8‐diyl‐2,5‐thiophene) (PZQT) have been synthesized and characterized. PZQP and PZQT have optical band gaps of 2.44 and 1.76 eV, respectively. Both polymers showed highly reversible electrochemical reduction, with an electron affinity of 3.6 eV for PZQP and 3.8 eV for PZQT. The electronic structures of PZQP, PZQT, and related poly(pyrazinoquinoxaline)s, were calculated by density functional theory and compared with the experimental results.

Molecular structure and reduction cyclic voltammogram of PZQP.     

GaxPy(x+y=8)及其阴离子团簇的结构与性质的DFT研究

用密度泛函理论方法对半导体二元微团簇GaxPy和GaxPy−(x+y=8)的几何结构、电子态、能量等进行了计算, 在B3LYP/6-311+G(2df)水平下完成结构优化和频率分析. 讨论了电荷诱导结构发生变化情况, 与中性团簇相比, 在阴离子团簇中, Ga—P键较P—P键有利于形成. 预测了未知Ga1P7−、Ga2P6−、Ga3P5−、Ga6P2−和Ga7P1−化合物的最稳定结构存在的可能性, 得出在GaxPy和GaxPy−(x+y=8)中, Ga4P4和Ga4P4−比较稳定. 给出了两种能差即绝热电子亲合势(ΔEAEA)和垂直电离能(ΔEVDE), 并与相关文献作比较. Ga4P4和Ga5P3的绝热电子亲合势与实验值相当吻合. 布居分析表明, 磷化镓团簇的成键属于混合键型.     

Assessing the role of Hartree‐Fock exchange,correlation energy and long range corrections in evaluating ionization potential,and electron affinity in density functional theory

Accurate determination of ionization potentials (IPs), electron affinities (EAs), fundamental gaps (FGs), and HOMO, LUMO energy levels of organic molecules play an important role in modeling and predicting the efficiencies of organic photovoltaics, OLEDs etc. In this work, we investigate the effects of Hartree Fock (HF) Exchange, correlation energy, and long range corrections in predicting IP and EA in Hybrid Functionals. We observe increase in percentage of HF exchange results in increase of IPs and decrease in EAs. Contrary to the general expectations inclusion of both HF exchange and correlation energy (from the second order perturbation theory MP2) leads to poor prediction. Range separated Hybrid Functionals are found to be more reliable among various DFT Functionals investigated. DFT Functionals predict accurate IPs whereas post HF methods predict accurate EAs. © 2017 Wiley Periodicals, Inc.     

Theoretical Investigation of 5d-Metal Monocarbides

Bond distances, vibrational frequencies, electron affinities, ionization potentials and dissociation energies of the title molecules in neutral, positively and negatively charged ions were studied by use of density functional method. The calculated results were compared with previous theoretical and experimental studies. Ground states for each molecule were assigned. It was found that for some molecules, low-lying state, in which the energy is much close to the ground state, was obtained. In this case, further studies both experimentally and theoretically are necessary in order to find the true global minimum.     

金钯二元小团簇的几何结构与电子性质

在UBP86/LANL2DZ和UB3LYP/def2-TZVP水平下详细研究了AumPdn(m+n≤6)团簇的几何结构和电子性质.阐明了团簇的结构特征、平均结合能、垂直电离势、垂直电子亲和能、电荷转移以及成键特征.除单取代混合团簇(AunPd和AuPdn,n=5或6)外,五和六原子混合团簇中钯原子趋于聚集到一起形成Pdcore,金原子分布在Pdcore周围形成PdcoreAushell结构.含一个和两个钯原子团簇的电子性质与纯金团簇类似,呈现一定奇偶振荡.混合团簇的电子性质,如最高占据分子轨道(HOMO),最低未占据分子轨道(LUMO),垂直电离势,垂直电子亲和能,Fermi能级和化学硬度等均与团簇空间结构和金、钯原子数之比直接相关.混合团簇中存在钯原子到金原子间的电荷转移,表明团簇中存在明显金钯间成键作用.分析团簇的电荷分布、前线轨道和化学硬度表明,金钯混合团簇对小分子如O2、H2和CO等的反应活性要强于纯金团簇.     

Assessment of quantum‐chemical methods for electronic properties and geometry of signaling biomolecules

A reasonable balance between accuracy and feasibility of quantum‐chemical methods depends on the complexity of the molecular system and the scientific goals. Six series of indole‐, naphthalene‐, phenol‐, benzoic‐, phenoxy‐, other auxin‐derivatives, and a test set of similar organic molecules have been chosen for an assessment of 13 density functional and semi‐empirical molecular orbital methods with respect to electronic and structural properties. The accuracy and precision of HOMO/LUMO calculations are determined by comparison with experimental ionization potentials and electron affinities. Further comparison was performed at atomic level by covariance analysis. The methods KMLYP, MSINDO, and PM3 are precise and accurate for the whole set of molecules. The method AM1 offers comparable accuracy with the exception of electron affinities of indole derivatives, where significant deviations from experiment were observed. Geometrical properties were best reproduced with the semi‐empirical method MSINDO. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Quantum chemical study of the autoxidation of ascorbate

Reactions involved in the autoxidation of ascorbate have been investigated with quantum chemical first‐principles and ab initio methods. Reaction energies and Gibbs energies of the reactions were calculated at the density functional theory level applying the gradient‐corrected BP86 and the hybrid B3LYP functionals together with def2‐TZVP basis sets. Results of single‐point CC2, CCSD, and CCSD(T) calculations were used for calibration of the density functional theory data and show excellent agreement with the B3LYP values. Based on the Gibbs energy ascorbic acid AscH₂ is found to be the energetically lowest species in aqueous solution, whereas the monoanion ascorbate AscH is the most abundant one near pH = 7. Asc was found to be the preferred reducing agent for autoxidation and oxidation processes. The results also support a metal‐catalyzed synthesis of the reactive oxygen species H₂O₂ according to a redox cycling mechanism proposed in literature. © 2016 Wiley Periodicals, Inc.     

Structural,Electronic, Reactivity,and Conformational Features of 2,5,5-Trimethyl-1,3,2-diheterophosphinane-2-sulfide,and Its Derivatives: DFT,MEP, and NBO Calculations

In this study, we used density functional theory (DFT) and natural bond orbital (NBO) analysis to determine the structural, electronic, reactivity, and conformational features of 2,5,5-trimethyl-1,3,2-di-heteroatom (X) phosphinane-2-sulfide derivatives (X = O (compound 1), S (compound 2), and Se (compound 3)). We discovered that the features improve dramatically at 6-31G** and B3LYP/6-311+G** levels. The level of theory for the molecular structure was optimized first, followed by the frontier molecular orbital theory development to assess molecular stability and reactivity. Molecular orbital calculations, such as the HOMO–LUMO energy gap and the mapping of molecular electrostatic potential surfaces (MEP), were performed similarly to DFT calculations. In addition, the electrostatic potential of the molecule was used to map the electron density on a surface. In addition to revealing molecules’ size and shape distribution, this study also shows the sites on the surface where molecules are most chemically reactive.     

Interesting properties of Thomas–Fermi kinetic and Parr electron–electron‐repulsion DFT energy functional generated compact one‐electron density approximation for ground‐state electronic energy of molecular systems

The reduction of the electronic Schrodinger equation or its calculating algorithm from 4N‐dimensions to a (nonlinear, approximate) density functional of three spatial dimension one‐electron density for an N‐electron system, which is tractable in the practice, is a long desired goal in electronic structure calculation. If the Thomas‐Fermi kinetic energy (～∫ρ^5/3d r ₁) and Parr electron–electron repulsion energy (～∫ρ^4/3d r ₁) main‐term functionals are accepted, and they should, the later described, compact one‐electron density approximation for calculating ground state electronic energy from the 2nd Hohenberg–Kohn theorem is also noticeable, because it is a certain consequence of the aforementioned two basic functionals. Its two parameters have been fitted to neutral and ionic atoms, which are transferable to molecules when one uses it for estimating ground‐state electronic energy. The convergence is proportional to the number of nuclei (M) needing low disc space usage and numerical integration. Its properties are discussed and compared with known ab initio methods, and for energy differences (here atomic ionization potentials) it is comparable or sometimes gives better result than those. It does not reach the chemical accuracy for total electronic energy, but beside its amusing simplicity, it is interesting in theoretical point of view, and can serve as generator function for more accurate one‐electron density models. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

Benchmark Calculations on the Atomization Enthalpy, Geometry and Vibrational Frequencies of UF6 with Relativistic DFT Methods

Benchmark calculations on the molar atomization enthalpy, geometry, and vibrational frequencies of uranium hexafluoride （UF6） have been performed by using relativistic density functional theory （DFT） with various levels of relativistic effects, different types of basis sets, and exchange-correlation functionals. Scalar relativistic effects are shown to be critical for the structural properties. The spin-orbit coupling effects are important for the calculated energies, but are much less important for other calculated ground-state properties of closed-shell UF6. We conclude through systematic investigations that ZORA- and RECP-based relativistic DPT methods are both appropriate for incorporating relativistic effects. Comparisons of different types of basis sets （Slater, Gaussian, and plane-wave types） and various levels of theoretical approximation of the exchange-correlation functionals were also made.