Molecular Ionization Energy Research Articles

Charge Separation in Water on Strong Impacts and Recombination of Dispersed Ions

Charge separation is a general phenomenon in nature. There has been vivid speculation and discussion about the mechanism of charge separation in condensed matter on strong impacts at small energies. Here we show that charge separation naturally occurs if water aggregates with embedded charge carriers, e.g. ions, encounter a high energy impact even though no plasma occurs and the involved kinetic energies are much below any molecular ionization energy. We find that the charge distribution in the fragments resulting from a strong impact can simply be described by a three step model.The first level of the model is a simple statistical description of the resulting charge distribution at low salt concentrations by making usage of the Poisson distribution. The second step involves the mutual interaction between the charge particles in the condensed matter, which allows us to describe the charge process at higher salt concentrations. We achieved this by using implicit water Monte Carlo Simulation methods of the charged particles. Finally we included the full dynamics of the separation process into our model by using all-atom non-equilibrium Molecular Dynamics Simulations to describe the charge separation at high salt concentrations and high separation process velocities.We present a microscopic model of the charging mechanism of fragments, that contributes to the understanding of a larger range of phenomena related to charges and charge separation in Nature.To test our model we describe the ion yield of laser desorption experiments, i.e. LILBID, at different salt concentrations over six orders of magnitude. To accommodate for the specific setup of the experiment, we not only model the initial charge separation with our microscopic model but also account for ion recombination, which occurs between ion desorption and final ion detection.

Electronic structure and stabilities of Ni-doped germanium nanoclusters: a density functional modeling study

The present study reports the geometry, electronic structure, growth behavior and stability of neutral and ionized nickel encapsulated germanium clusters containing 1-20 germanium atoms within the framework of a linear combination of atomic orbital density functional theory (DFT) under a spin polarized generalized gradient approximation. In the growth pattern, Ni-capped Gen and Ni-encapsulated Gen clusters appear mostly as theoretical ground state at a particular size. To explain the relative stability of the ground state clusters, variation of different parameters, such as average binding energy per atom (BE), embedding energy (EE) and fragmentation energy (FE) of the clusters, were studied together with the size of the cluster. To explain the chemical stability of the clusters, different parameters, e.g., energy gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gap), ionization energy (IP), electron affinity (EA), chemical potential (μ), chemical hardness (η), and polarizability etc. were calculated and are discussed. Finally, natural bond orbital (NBO) analysis was applied to understand the electron counting rule applied in the most stable Ge10Ni cluster. The importance of the calculated results in the design of Ge-based superatoms is discussed.

Predicting the Sites and Energies of Noncovalent Intermolecular Interactions Using Local Properties

Feed-forward artificial neural nets have been used to recognize H-bond donor and acceptor sites on drug-like molecules based on local properties (electron density, molecular electrostatic potential and local ionization energy, electron affinity, and polarizability) calculated at grid points around the molecule. Interaction energies for training were obtained from B97-D and ωB97X-D/aug-cc-pVDZ density-functional theory calculations on a series of model central molecules and H-bond acceptor and donor probes constrained to the grid points used for training. The resulting models provide maps of both classical and unusual H- and halogen-bonding sites. Note that these reactions result even though only classical H-bond donors and acceptors were used as probes around the central molecules. Some examples demonstrate the ability of the models to take the electronics of the central molecule into consideration and to provide semiquantitative estimates of interaction energies at low computational cost.

Investigation of retention behavior of polychlorinated biphenyl congeners on 18 different HRGC columns using molecular surface average local ionization energy descriptors

In this paper, based on the general interaction properties function (GIPF) family descriptors computed at the B3LYP/6-31G* level in Gaussian98 software, a significant quantitative structure–retention relationship (QSRR) models for the high resolution gas chromatographic relative retention time (HRGC-RRT) of all PCB congeners on 18 different HRGC capillary columns were constructed by using multiple linear regression (MLR) analysis, following the guidelines for development and validation of QSRR models. By means of the elimination selection stepwise regression algorithms, the molecular surface average local ionization energy was selected as one-parameter univariate linear regression to develop a QSRR model for prediction of GC-RRT of PCBs on each stationary phase. The accuracy of all developed models was confirmed using different types of internal and external procedures. A successful interpretation of the complex relationship between HRGC-RRTs of PCBs and the chemical structures was achieved by QSRR.

Energy-Level Alignment in 4′-Substituted Stilbene-4-thiolate Self-Assembled Monolayers on Gold

Molecular energy-level alignment around the Fermi level in self-assembled monolayers of E-stilbene-4-thiolate (SAM1), E-4′-(ethoxy)stilbene-4-thiolate (SAM2), and E-4′-(dimethylamino)stilbene-4-thiolate (SAM3) on Au(111) was studied by ultraviolet photoelectron spectroscopy. A comparison of the measured hole-injection barriers into SAM1−3 with the electrochemically estimated molecular ionization energies reveals that the influence of the 4′-substituent in the stilbene backbone on the hole-injection barrier is greatly suppressed. While predicted theoretically for a variety of densely packed π-conjugated thiolate monolayers before, we here provide conclusive experimental evidence for this phenomenon. The obtained results are compared to periodic density-functional theory calculations and are discussed in the light of electrostatic properties of dipolar monolayers.

충격파 내에서 형성되는 아르곤 기체의 운동 에너지 분포와 속도 분포에 대한 비평형 분자동역학 모의실험 연구

A series of nonequilibrium molecular dynamics(NEMD) simulations are performed to investigate the kinetic energy and velocity distributions of molecules in shock waves. In the simulations, argon molecules are used as a medium gas through which shock waves are propagating. The kinetic energy distribution profiles reveals that as a strong shock wave whose Mach number is 27.1 is applied, 39.6% of argon molecules inside the shock wave have larger kinetic energy than molecular ionization energy. This indicates that an application of a strong shock wave to argon gas can give rise to an intense light. The velocity distribution profiles in z direction along which shock waves propagate clearly represent two Maxwell-Boltzmann distributions of molecular velocities in two equilibrium regions and one bimodal velocity distribution profile that is attributed to a nonequilibrium region. The peak appearing in the directional temperature in z direction is discussed on a basis of the bimodal velocity distribution in the nonequilibrium region.

Charge Separation and Isolation in Water and Ice Particles on Strong Impacts

Charge separation is a general phenomenon in nature. There has been vivid speculation and discussion about the mechanism of charge separation in condensed matter on strong impacts at small energies. Here we show that charge separation naturally occurs if water aggregates or particles with embedded charge carriers, e.g. ions, encounter a high energy impact even though no plasma occurs and the involved kinetic energies are much below any molecular ionization energy. We find that the charge distribution in the fragments resulting from a strong impact can simply be described by a three step model. The first level of the model is a simple statistical description of the resulting charge distribution at low salt concentrations by making usage of the Poisson distribution. The second step of describing the charge distribution of the dispersed fragments involves the mutual interaction between the charge particles in the condensed matter, which allows us to describe the charge process at higher salt concentrations. We achieved this by using implicit water Monte Carlo Simulation methods of the charged particles. Finally we included the full dynamics of the separation process into our model by using non-equilibrium Molecular Dynamics Simulations to describe the charge separation at high salt concentrations and high separation process velocities. We present a microscopic model of the charging mechanism of fragments, that contributes to the understanding of a larger range of phenomena related to charges and charge separation in Nature. With this model we shed light on the charge mechanism of laser desorption experiments and discuss the impact of the current results for particle detection in space and possible implications for lightning formation in the atmosphere.

Optical excitation energies, Stokes shift, and spin-splitting of C24H72Si14

As an initial step toward the synthesis and characterization of sila-diamondoids, such as sila-adamantane (Si(10)H(16),T(d)), the synthesis of a fourfold silylated sila-adamantane molecule (C(24)H(72)Si(14),T(d)) has been reported in literature [Fischer et al., Science 310, 825 (2005)]. We present the electronic structure, ionization energies, quasiparticle gap, and the excitation energies for the Si(14)(CH(3))(24) and the exact silicon analog of adamantane Si(10)H(16) obtained at the all-electron level using the delta-self-consistent-field and transitional state methods within two different density functional models: (i) Perdew-Burke-Ernzerhof generalized gradient approximation and (ii) fully analytic density functional (ADFT) implementation with atom dependent potential. The ADFT is designed so that molecules separate into atoms having exact atomic energies. The calculations within the two models agree well, to within 0.25 eV for optical excitations. The effect of structural relaxation in the presence of electron-hole-pair excitations is examined to obtain its contribution to the luminescence Stokes shift. The spin-influence on exciton energies is also determined. Our calculations indicate overall decrease in the absorption, emission, quasiparticle, and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, ionization energies, Stokes shift, and exciton binding energy when passivating hydrogens in the Si(10)H(16) are replaced with electron donating groups such as methyl (Me) and trimehylsilyl (-Si(Me)(3)).

Semiconductor Properties of Perylene Diimide Derivatives

Density functional theory (DFT) calculations were carried out to study the charge transfer properties of N, N'-bisperylene-3, 4, 9, 10-tetracarboxylic diimide (1), N,N'-bis (3-chlorobenzyl) peiylene-3, 4, 9, 10-tetracarboxylic diimide (2), N,N'-bis (3-fluorobenzyl) perylene-3, 4, 9, 10-tetracarboxylic diimide (3), and N,N'-bis (3, 3-difluorobenzyl) perylene 3, 4, 9, 10-tetracarboxylic diimide (4) for use as organic field effect transistors (OFETs). The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies, ionization energy (IE), electron affinity (EA), and reorganization energy (A) were investigated for these compounds. Corresponding to energy changes in the HOMO and LUMO for 2-4, the introduction of chlorobenzyl or fluorobenzyl groups leads to high adiabatic electron affinity (EA(subscript a)) values for 2-4. The transfer integral (V) and field effect transistor (FET) properties for the four compounds with known crystal structures were calculated based on Marcus electron transfer theory. The calculated results reveal that a very small injection barrier exists relative to the Au source-drain electrode of 1-4 for electrons, producing good potential n-type semiconductors. Intrinsic electron transfer mobilities (μ(subscript -)) of 5.39, 0.59, 0.023, and 0.17 cm^2 were calculated for compounds 1-4, respectively. The high intrinsic electron mobilities for 1-4 were rationalized by examining the changes in geometric structure upon reduction and charge transfer integral for the different transfer modes in crystal 3.

Comment on “Assessing the Efficacy of Nonsteroidal Anti-Inflammatory Drugs Through the Quantum Computation of Molecular Ionization Energies”

Comment on “Assessing the Efficacy of Nonsteroidal Anti-Inflammatory Drugs Through the Quantum Computation of Molecular Ionization Energies”

Correlations of the Stability, Static Dipole Polarizabilities, and Electronic Properties of Yttrium Clusters

Static dipole polarizabilities for the ground-state geometries of yttrium clusters (Yn, n < or = 15) are investigated by using the numerically finite field method in the framework of density functional theory. The structural size dependence of electronic properties, such as the highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) gap, ionization energy, electron affinity, chemical hardness and softness, etc., has been determined for yttrium clusters. The energetic analysis, minimum polarizability principle, and principle of maximum hardness are used to characterize the stability of yttrium clusters. The correlations of stability, static dipole polarizabilities, and electronic properties are analyzed especially. The results show that static polarizability and electronic structure can reflect obviously the stability of yttrium clusters. The static polarizability per atom decreases slowly with an increase in the cluster size and exhibits a local minimum at the magic number cluster. The ratio of the mean static polarizability to the HOMO-LUMO gap has a much lower value for the most stable clusters. The static dipole polarizabilities of yttrium clusters are highly dependent on their electronic properties and are also partly related to their geometrical characteristics. A large HOMO-LUMO gap of an yttrium cluster usually corresponds to a large dipole moment. Strong correlative relationships of the ionization potential, softness, and static dipole polarizability are observed for yttrium clusters.

An explicitly spin-free compact open-shell coupled cluster theory using a multireference combinatoric exponential ansatz: Formal development and pilot applications

In this paper, we present a comprehensive account of an explicitly spin-free compact state-universal multireference coupled cluster (CC) formalism for computing the state energies of simple open-shell systems, e.g., doublets and biradicals, where the target open-shell states can be described by a few configuration state functions spanning a model space. The cluster operators in this formalism are defined in terms of the spin-free unitary generators with respect to the common closed-shell component of all model functions (core) as vacuum. The spin-free cluster operators are either closed-shell-like n hole-n particle excitations (denoted by T(mu)) or involve excitations from the doubly occupied (nonvalence) orbitals to the singly occupied (valence) orbitals (denoted by S(e)(mu)). In addition, there are cluster operators with exchange spectator scatterings involving the valence orbitals (denoted by S(re)(mu)). We propose a new multireference cluster expansion ansatz for the wave operator with the above generally noncommuting cluster operators which essentially has the same physical content as the Jeziorski-Monkhorst ansatz with the commuting cluster operators defined in the spin-orbital basis. The T(mu) operators in our ansatz are taken to commute with all other operators, while the S(e)(mu) and S(re)(mu) operators are allowed to contract among themselves through the spectator valence orbitals. An important innovation of this ansatz is the choice of an appropriate automorphic factor accompanying each contracted composite of cluster operators in order to ensure that each distinct excitation generated by this composite appears only once in the wave operator. The resulting CC equations consist of two types of terms: a "direct" term and a "normalization" term containing the effective Hamiltonian operator. It is emphasized that the direct term is almost quartic in the cluster amplitudes, barring only a handful of terms and termination of the normalization term depends on the valence rank of the effective Hamiltonian operator and the excitation rank of the cluster operators at which the theory is truncated. Illustrative applications are presented by computing the state energies of neutral doublet radicals and doublet molecular cations and ionization energies of neutral molecules and comparing our results with the other open-shell CC theories, benchmark full CI results (when available) in the same basis, and the experimental results. Highly encouraging results show the efficacy of the method.

Density Functional Theory Study on the Semiconducting Properties of Metal Phthalocyanine Compounds: Effect of Axially Coordinated Ligand

To investigate the effect of axially coordinated ligand(s) on the semidconducting properties of metal phthalocyanine complexes, density functional theory (DFT) calculations were carried out in terms of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy, ionization energy (IE), electronic affinity (EA), and reorganization energy (lambda) of F(2)SnPc, Cl(2)SnPc, I(2)SnPc, OSnPc, OVPc, and Cl(2)TiPc. For the purpose of comparative studies, calculation on SnPc without axially coordinated ligand has also been conducted. The electronic couplings (V) and the charge transfer mobilities for the electron of metal phthalocyanine compounds with reported single crystal structures for Cl(2)SnPc, I(2)SnPc, and Cl(2)TiPc are also calculated. Comparison of the calculated results of SnPc with F(2)SnPc, Cl(2)SnPc, I(2)SnPc, and OSnPc indicates that introduction of axially coordinated ligand(s) obviously lowers the HOMO and LUMO energies of metal phthalocyanine complexes but does not change their energy difference, which results in an increase in their electronic affinity and ionization energy for metal phthalocyanine complexes containing axially coordinated ligand(s). This result is responsible for the decrease in the electron injection barrier and increase in the hole injection barrier of metal phthalocyanine complexes containing axially coordinated ligand(s) in comparison with metal phthalocyanine complexes without axially coordinated ligand, leading to the change in the nature of semiconductivity from p-type for SnPc to n-type for F(2)SnPc, Cl(2)SnPc, I(2)SnPc, and OSnPc. Because of the smaller electronegativity of V(IV) than that of Sn(IV), OVPc is revealed to display p-type semiconductivity in terms of electronic affinity (EA(v)). In contrast, Cl(2)TiPc is revealed to show n-type semiconductivity because of its large electronic affinity (EA(v)). The present work, representing the first theoretical effort toward understanding the effect of axially coordinated ligand(s) on the semiconducting properties of metal phthalocyanine complexes, will be helpful for designing and preparing novel phthalocyanine semidconductors with good organic field effect transistor (OFET) performance.

Computational Prediction of Antibody Binding Sites on Tetracycline Antibiotics: Electrostatic Potentials and Average Local Ionization Energies on Molecular Surfaces

Enzyme linked immunosorbent assay (ELISA) was used for the analysis of tetracycline, chlortetracycline, oxytetracycline, and their transformed compounds in environmental water samples. The antibodies employed in ELISA showed high relative affinity for tetracycline, epitetracycline, chlortetracycline, and epichlortetracycline as compared to anhydrotetracycline, epianhydrotetracycline, and anhydrochlortetracycline. The specificity and crossreactivity of these antibodies are discussed in relation to the electrostatic potentials and average local ionization energies computed on the molecular surfaces of tetracycline antibiotics and their transformed compounds with an objective of identifying common features as well as differences that may be related to the experimentally observed variation in cross-reactivity values. The computations were performed at both the HF/STO-3G and HF/6-31+G* levels using the Gaussian 98 program. The results in this study are based upon molecular electrostatic potentials and local ionization energies computed on isodensity molecular surfaces. The surface electrostatic potentials are characterized in terms of a group of statistically defined quantities, which include the average deviation, the positive, negative, and total variances, positive and negative surface extrema, and a parameter indicating the degree of electrostatic balance.

Adsorption-Induced Intramolecular Dipole: Correlating Molecular Conformation and Interface Electronic Structure

The interfaces formed between pentacene (PEN) and perfluoropentacene (PFP) molecules and Cu(111) were studied using photoelectron spectroscopy, X-ray standing wave (XSW), and scanning tunneling microscopy measurements, in conjunction with theoretical modeling. The average carbon bonding distances for PEN and PFP differ strongly, that is, 2.34 A for PEN versus 2.98 A for PFP. An adsorption-induced nonplanar conformation of PFP is suggested by XSW (F atoms 0.1 A above the carbon plane), which causes an intramolecular dipole of approximately 0.5 D. These observations explain why the hole injection barriers at both molecule/metal interfaces are comparable (1.10 eV for PEN and 1.35 eV for PFP) whereas the molecular ionization energies differ significantly (5.00 eV for PEN and 5.85 eV for PFP). Our results show that the hypothesis of charge injection barrier tuning at organic/metal interfaces by adjusting the ionization energy of molecules is not always readily applicable.

Molecular structure, atomization energy, ionization energy, electron affinity and vibrational spectrum of SiX2(X = F, Cl, Br, I) by theoretical methods

The molecular structure, atomization energy, ionization energy, electron affinity and vibrational spectra of silicon dihalides, SiX2 (X = F, Cl, Br, I), have been obtained using theoretical methods in the gas phase. The neutral dihalides, their cations and anions have been studied in C2v symmetry. The neutral species have been considered in both the 1 A1 singlet and 3 B1 triplet states whereas the cations (SiX2 +) and anions (SiX2 −) have been considered in the 2 A1 and 2 B1states, respectively. The methods used are Moller-Plesset perturbation theory (MP2), density functional theory (DFT), Gaussian-2 (G2) and complete basis set methods (CBS-4 and CBS-Q). The functional used for the DFT method is B3LYP. The basis sets used are 6-311++G(d,p) for all atoms except that 6-311G(d,p) has been used for iodine atom only. The silicon dihalides, their cations and anions have been fully optimized using MP2 and DFT methods. Single point energy computations (G2, CBS-4M and CBS-Q) have been performed except for silicon ...

Alkali metals in perylene-3,4,9,10-tetracarboxylicdianhydride thin films

n -type doping of the molecular organic semiconductor perylene-3,4,9,10-tetracarboxylicdianhydride (PTCDA) by sodium, potassium, and cesium was carried out. The chemical properties of the doping processes were investigated by means of x-ray photoemission and infrared absorption spectroscopy. Simultaneously the evolution of the occupied electronic states around the transport gap was monitored by ultraviolet photoemission spectroscopy. It was found that the doping ratio depends on the ionization energy of the alkali metal, in particular if compared with the highest occupied molecular orbital ionization energy of the formed alkali-PTCDA complex. Additionally, only in the case of cesium doping, an averaged ratio of two alkali metal atoms per PTCDA was found at the surface. In the case of sodium and potassium, averaged surface doping ratios of only 1.3±0.1 alkali metal atoms per PTCDA molecule can be reached. However, in the bulk phase, nearly complete doping can be reached by all three alkali metals.

Molecular Rydberg States and Ionization Energy Studied by Two‐Photon Resonant Ionization Spectroscopy

AbstractIn this article, I will review the excited valence/Rydberg states and ionization energies of vinyl chloride, propyne, and allyl radical that we have examined recently in our laboratory by 2+1 resonance enhanced multiphoton ionization (REMPI) spectroscopy. In these studies, we have emphasized spectroscopic investigations from the first excited electronic states to the first ionization energies of the molecules and radicals of interest. In spectroscopic analysis, successful electronic identifications have been facilitated with theoretical (ab initio and density functional) calculations. In particular, we have applied calculated Franck‐Condon factors to assist vibrational assignment for experimental vibronic spectra. The spectroscopic studies of these polyatomic excited valence/Rydberg states help us to illuminate the photodissociation pathways and to manifest the complicated chemical‐reaction mechanisms due to the multi‐dimensionality in polyatomic molecular potential energy surfaces.

The vacuum ultraviolet laser excitation spectra for free ion-pair (X+ + Y–) formation from jet-cooled I2 and ICl

The energy difference between the threshold for free ion-pair formation (X+ + Y−) and the molecular ionization energy (XY+) is relatively large in I2 and ICl. Photodissociation to free ion-pairs in this energy region has been probed by vacuum ultraviolet laser radiation generated by four-wave mixing. The negative ion excitation spectra are highly structured and closely follow the one-photon absorption cross-sections. Several Rydberg series are identified, the f series being particularly prominent. Direct absorption to the free ion-pair continuum is negligible in this region and all of the Rydberg states that are accessed act as efficient doorway states to ion-pair production.

The changing features of the molecular intrinsic characteristic contours of H 2 molecule in the ground and first excited states calculated by an ab initio method

The potential acting on an electron in a molecule (PAEM) is formulated, and then given by the concrete expression via CI wavefunction. The molecular intrinsic characteristic contour (MICC) of a molecule is defined as a surface that consists of all the classical turning points of the electron motion within the molecule. At every one of those points the PAEM is equal to the negative of the molecular first ionization energy. MICCs of H 2 molecule in both its ground state 1Σ g + and first excited state 3Σ u + at a series of internuclear distances were calculated by means of the MELD ab initio program with full-CI calculation and a separated program. And then the changing features were sketched for the first time. This may provide a fundamental insight into the spatial evolution of the molecular shape during bond-forming and/or bond-breaking processes.