Selected Publications of Jerry L. Whitten

C.-Y. Qin and J. L. Whitten, Adsorption of O, H, OH and H2O on Ag(100), J. Phys. Chem. B (2005), 109(18), 8852-8856.

Kokh, Daria B.; Buenker, Robert J.; Liebermann, Heinz-Peter; Pichl, Lukas; Whitten, Jerry L. Theoretical Study of the CH2 + O Photodissociation of Formaldehyde Adsorbed on the Ag(111) Surface. Journal of Physical Chemistry B (2005), 109(38), 18070-18080.

Lucovsky, Gerald; Fulton, C. C.; Zhang, Y.; Zou, Y.; Luning, J.; Edge, L. F.; Whitten, J. L.; Nemanich, R. J.; Ade, H.; Schlom, D. G.; Afanase'v, V. V.; Stesmans, A.; Zollner, S.; Triyoso, D.; Rogers, B. R. Conduction band-edge states associated with the removal of d-state degeneracy by the Jahn-Teller effect. IEEE Transactions on Device and Materials Reliability (2005), 5(1), 65-83.

Daria B. Kokh, Robert J. Buenker, and Jerry L. Whitten. Trends in adsorption of open-shell atoms and small molecular fragments on the Ag(111) surface, Surface Science 600 (2006), 5104–5113

Qin, Changyong; Sremaniak, Laura S.; Whitten, Jerry L. CO adsorption on Ag(100) and Ag/MgO(100). Journal of Physical Chemistry B (2006), 110(23), 11272-11276.

Laura S. Sremaniak, Jerry L. Whitten, Matthew J. Truitt, Jeffery L. White. Weak Hydrogen Bonding Can Initiate Alkane C-H Bond Activation in Acidic Zeolites, J. Phys. Chem. B (2006), 110, 20762-20764.

C.M. Osburn, S.A. Campbell, A. Demkov, E. Eisenbraun, E. Garfunkel, T. Gustafsson, A.I. Kingon, J. Lee, D.J. Lichtenwalner, G. Lucovsky, T.P. Ma, J.P. Maria, V. Misra, R.J. Nemanich, G.N. Parsons, D.G. Schlom, S. Stemmer, R.M. Wallace, and J. Whitten. Materials and Processes for High k Gate Stacks: Results from the FEP Transition Center, ECS Transactions, 3(3), 389 (2006)

L. S. Sremaniak and J. L. Whitten, Theoretical treatment of excited electronic states of adsorbates on metals: electron attachment to CO2 adsorbed on Pt(111), Surface Science, (2007), 601, 3755-3759.

G. Lucovsky and J. L. Whitten, Metal Gate Electrodes: Theoretical Studies of Zr/ZrO2 and Hf/HfO2 interfaces, Surface Science (2007), 601, 4138-4143.

Kokh, D. B.; Buenker, R. J.; Liebermann, H.-P.; Whitten, J. L. Theoretical Study of the Photoinduced C-H Bond Cleavage in Formaldehyde Adsorbed on the Ag(111) Surface, J. Phys. Chem. C. (2007) 111(27), 9914-9918.

L. S. Sremaniak and J. L. Whitten, Theoretical treatment of excited electronic states of adsorbates on metals: electron attachment to CO2 adsorbed on K-modified Pt(111), Surface Science, 602 (4), 834-842, (2008).

Yu Zhang and Jerry L. Whitten, Photoinduced dissociation of water and transport of H between silver clusters, J. Phys. Chem. A, 112, 6358-6363 (2008).

Yu Zhang and J. L. Whitten, Photoemission into water adsorbed on metals: probing dissociative electron transfer using theory, International J. Quantum Chemistry (2009), 109(15), 3541-3551.

B. N. Papas and J. L. Whitten, Dissociation of water on a palladium nanoparticle, International Journal of Quantum Chemistry, 110, 3072–3079 (2010).

Takashi Tsuchiya and Jerry L. Whitten, Theoretical Study of the Molecular and Electronic Structures of TiO4H4, Ti2O7H6, and Ti2O6H4, J. Phys. Chem. C, 2011, 115 (5), pp 1635–1642.

Takashi Tsuchiya and Jerry L. Whitten, Configuration interaction study of the ground and
excited states of TiO2 ring structures, Journal of Chemical Physics, 134, 114701-7 (2011).

Hyungtak Seo, L. Robert Baker, Antoine Hervier, Jinwoo Kim, J. L. Whitten, and Gabor A. Somorji, Generation of Highly n-Type Titanium Oxide Using Plasma Fluorine Insertion, Nano Lett., 2011, 11 (2), pp 751–756.

Abstracts of Recent Work

Theoretical treatment of excited electronic states of adsorbates on metals: electron attachment to CO2 adsorbed on Pt(111)

L. S. Sremaniak and J. L. Whitten, Surface Science, (2007) 601, 3755-3759.

Abstract. Photochemistry involving adsorbates on metals often proceeds by photoexcitation of the metal followed by transient attachment of photo emitted electrons to the adsorbate. First principles theoretical methods suitable for describing electronic states embedded in a near continuum of metal to metal excitations are described and an application to electron attachment to CO2 adsorbed on Pt(lll) is reported. Wavefunctions are constructed by ab initio configuration interaction methods which allow a rigorous resolution of states and differentiation between competing pathways of molecular desorption and dissociation. An embedding theory is used to achieve high accuracy in the adsorbate-surface region. The overall process can be understood as formation of an electron attached state at an energy lower than the work function of the metal, localization of the metal hole and attraction of the charged adsorbate to the metal. Optimum geometries are calculated and pathways between these geometries determine whether molecules will desorb, dissociate by bond rupture directly in the excited electronic state, or dissociate after return to the ground state potential energy surface via vibrational processes. The influence of a coadsorbed potassium electron donor atom on the energy required to form the electron attachment state is also reported.

Weak Hydrogen Bonding Can Initiate Alkane C-H Bond Activation in Acidic Zeolites

Laura S. Sremaniak, Jerry L. Whitten, Matthew J. Truitt, and Jeffery L. White. J. Phys. Chem., Phys. Chem. B (2006), 110, 20762-20764.

Abstract. Ab initio calculations at the Hartree-Fock self-consistent field/single determinant (SCF) and configuration interaction multi-determinant (CI) expansion levels have been used to show that isobutane primary C-H bond activation occurs via direct protium exchange with the zeolite surface via a weakly hydrogen-bonded complex. The calculated 15 kcal/mol activation barrier agrees with the 13.7 kcal/mol value from a recently reported experimental study (J. Am. Chem. Soc. 2006, 128, 1847-1852). Overall, the mechanism described in this contribution demonstrates that weak C-H to O hydrogen bonding leads to complexes at the zeolite acid site that can facilitate C-H bond activation.

Metal Gate Electrodes: Theoretical Studies of Zr/ZrO2 and Hf/HfO2 Interfaces

G. Lucovsky and J. L. Whitten, Surface Science (2007), 601, 4138-4143.

Abstract. Ab initio quantum mechanical calculations have been performed on cluster models of Zr/ZrO2 and Hf/HfO2 interfaces. The theoretical method is a first principles method in which an exact electrostatic Hamiltonian is employed, except for core electron effective potentials, and wavefunctions are constructed by a self-consistent-field (SCF) method in which ionic correlation is included by local configuration interaction (CI). The outcome of the calculations is a detailed prediction of the electronic structure of the interface from which electrical properties can be inferred; e.g., work function, surface dipoles, barriers to electron transport, etc. The results are compared with and also serve to calibrate electronegativity arguments that lead to predictions of surface dipole changes when Zr or Hf metals are deposited on the respective elemental oxides. In the present work the cluster describing the Zr/ZrO2 interface was embedded in an electrostatic field that simulates more distant Madelung contributions, and removes unphysical solutions as well.

Photoinduced dissociation of water and transport of H between silver clusters

Yu Zhang and Jerry L. Whitten, J. Phys. Chem. A, 112, 6358-6363 (2008).

Abstract. Theoretical electronic structure calculations are reported for the dissociation of water adsorbed on a 31 atom silver cluster, Ag31, and subsequent transfer of a H to a second Ag31 cluster leaving OH on the first cluster. Both ground and excited electronic state processes are considered for two choices of Ag cluster separation, 6.35 Å and 7.94 Å. The excited electronic state of interest is formed by photoemission of an electron from one Ag cluster and transient attachment of the photoemitted electron to the adsorbed water molecule. A very large energy barrier is found for the ground state process (3.53 eV at a cluster separation of 12.0 a.u.) while the barrier in the excited state is small (0.38 eV at a cluster separation of 12.0 a.u.). In the excited state, partial occupancy of an OH antibonding orbital facilitates OH stretch and concomitant movement of the negatively charged OH toward the electron hole in the metal cluster. The excited state pathway for dissociation of water and transfer of H begins with the formation of an excited electronic state at 3.59~3.82 eV. Stretch of the OH bond occurs with little change in energy (0.38~0.54 eV up to a stretch of 3.70 a.u.). In this region of OH stretch the molecule must return to the ground state potential energy surface to fully dissociate and to transfer H to the other Ag cluster. Geometry optimizations are carried out using a simplex algorithm and a semi-grid method. These methods allow the total energy to be calculated directly using configuration interaction theory.

Photoinduced dissociation of water adsorbed on a Ag cluster

Yu Zhang and Jerry L. Whitten, Theochem, accepted (2008).

Abstract. Theoretical electronic structure calculations are reported for the photoinduced dissociation of water adsorbed on a 31-atom silver cluster, Ag31 to produce H2 and adsorbed O. Both ground and excited electronic state processes are considered. The excited electronic state of interest is formed by photoemission of an electron from the Ag cluster and transient attachment of the electron to the adsorbed water molecule. A very large energy barrier for H2 formation (3.51 eV) is found for the ground state process while the barrier in the excited state is much smaller (0.47 eV). In the excited state, partial occupancy of an OH antibonding orbital facilitates OH stretch and the electron hole in the metal cluster stabilizes OH and O adsorbates. The excited state pathway for dissociation of water begins with the formation of an excited electronic state at 3.49 eV. Stretch of the OH bond up to 3.44 a.u. (1.82Å) occurs with little change in energy. In this region of OH stretch the molecule must return to the ground state potential energy surface to dissociate fully and to form H2. Geometry optimizations are carried out using a simplex algorithm which allows the total energy to be calculated using configuration interaction theory.

Theoretical treatment of excited electronic states of adsorbates on metals: electron attachment to CO2 adsorbed on K-modified Pt(111)

L. S. Sremaniak and J. L. Whitten, Surface Science, 602 (4), 834-842, (2008).

Abstract. Theoretical studies of photoinduced processes involving electron attachment to CO2 adsorbed on Pt(111) in the presence of a coadsorbed K atom are reported. First principles theoretical methods suitable for describing electronic states embedded in a near continuum of metal to metal excitations are described. Wavefunctions are constructed by ab initio configuration interaction methods which allow a rigorous resolution of states and differentiation between competing pathways of molecular desorption and dissociation. An embedding theory is used to achieve high accuracy in the adsorbate-surface region. Compared to CO2 adsorbed on Pt(111), the K promoter lowers the work function of the system from 5.6 to 5.2 eV and decreases the energy required to form the electron attached excited electronic state from 6.8 to 5.6 eV. However, stabilization of CO2 depends strongly on orientation and proximity to the K adatom. The most favorable pathway leading to dissociation requires that CO2 be adsorbed at a site that does not share Pt atoms with the K adsorption site i.e., at next nearest neighbor sites. As was found for Pt(111) without a K adatom, the dissociation pathway involves bending of CO2 in the excited state followed by either dissociation on the excited state surface where the barrier height is reduced from its value of 1.0 eV on the Pt surface to 0.34 eV. As is the case for the unmodified surface, dissociation could also occur after return to the ground state potential energy surface via vibrational processes.

Theoretical Studies of Surface Reactions on Metals and Electronic Materials*

J. L. Whitten, Abstract of research currently supported by the U.S. Department of Energy.

Abstract. This proposal describes the renewal of a theoretical research program on the structure and reactivity of molecules adsorbed on transition metal surfaces. A new direction of the work extends investigations to interfaces between solid surfaces, adsorbates and aqueous solutions and includes fundamental work on photoinduced electron transport into chemisorbed species and into solution. The goal is to discover practical ways to reduce water to hydrogen and oxygen using radiation comparable to that available in the solar spectrum. The work relates to two broad subject areas: photocatalytic processes and production of hydrogen from water. The objective is to obtain high quality solutions of the electronic structure of adsorbate-metal-surface-solution systems so as to allow activation barriers to be calculated and reaction mechanisms to be determined. An ab initio embedding formalism provides a route to the required accuracy. New theoretical methods developed during the previous grant period will be implemented in order to solve the large systems involved in this work. Included is the formulation of a correlation operator that is used to treat localized electron distributions such as ionic or regionally localized distributions. The correlation operator which is expressed as a two-particle projector is used in conjunction with configuration interaction.Photoemission, electron attachment to water followed by formation of H2 or transport of H to a second nanoparticle

Photoinduced dissociation of water adsorbed on a Ag cluster

Yu Zhang and Jerry L. Whitten, Journal of Molecular Structure: THEOCHEM, published online
26 January 2009 THEOCHEM (2009), 903(1-3), 28-33

Abstract. Theoretical electronic structure calculations are reported for the photoinduced dissociation of water adsorbed on a 31-atom silver cluster, Ag31 to produce H2 and adsorbed O. Both ground and excited electronic state processes are considered. The excited electronic state of interest is formed by photoemission of an electron from the Ag cluster and transient attachment of the electron to the adsorbed water molecule. A very large energy barrier for H2 formation (3.51 eV) is found for the ground state process while the barrier in the excited state is much smaller (0.47 eV). In the excited state, partial occupancy of an OH antibonding orbital facilitates OH stretch and the electron hole in the metal cluster stabilizes OH and O adsorbates. The excited state pathway for dissociation of water begins with the formation of an excited electronic state at 3.49 eV. Stretch of the OH bond up to 3.44 a.u. (1.82Å) occurs with little change in energy. In this region of OH stretch the molecule must return to the ground state potential energy surface to dissociate fully and to form H2. Geometry optimizations are carried out using a simplex algorithm which allows the total energy to be calculated using configuration interaction theory.

Photoemission into water adsorbed on metals: probing dissociative electron transfer using theory

Yu Zhang and J. L. Whitten, International J. Quantum Chemisty (2009), 109(15), 3541-3551.

Abstract. The photoinduced dissociation of water adsorbed on a silver nanoparticle is explored using theory to probe reaction pathways that produce hydrogen. Ab initio configuration theory is used to describe the systems. A formulation that allows excited electronic states embedded in a near continuum of lower energy states to be calculated accurately is described. Electron attachment of a photoemitted electron to adsorbed water can lead to the formation of H2 at a very low energy barrier with oxygen remaining on the Ag surface. A large energy barrier to form H2 plus adsorbed O is found for the ground state. The excited state has a much smaller barrier to OH stretch; however, to dissociate, the system must cross over from the excited state to the ground state potential energy surface. The cross over point is near the transition state for a ground state process. A characteristic feature of the excited state potential curve is an increase in energy in the early stages of OH stretch as the charge transfer state evolves from a state with considerable Rydberg character to one that has a typical OH antibonding molecular orbital. Another pathway releases a H atom leaving OH on the surface. Effects due to doping of a Ag nanoparticle with a K electron donor atom are compared with those caused by a Fermi level shift due to an applied potential. Results are also reported for electron transfer to a solvated lithium ion, Li(H2O)6+, near the surface of a silver particle. A steering mechanism is found that involves the interaction of a hydridic hydrogen formed after electron transfer with an acidic hydrogen of a second solvated water molecule.

Dissociation of Water on a Palladium Nanoparticle.

Brian N. Papas, Jerry L. Whitten, International Journal of Quantum Chemistry, 110, 3072–3079 (2010).

Abstract. Ab initio SCF-CI theory has been used to examine the interactions of a single water molecule with a 31-atom nanocluster of palladium. Calculations are performed on singly-charged cationic and anionic particles in addition to the neutral system to determine effects of charging on the adsorption energy of water and the barriers to dissociation. Penetration of the dissociated H through the surface layer into an interstitial subsurface site is also examined. Adsorption energies of an intact water molecule fall in the range 0.2–0.8 eV, while the barrier to dissociation into a subsurface site is in the range 1.4–2.1 eV depending on the charge of the metal particle. Calculations on the photoinduced dissociation of water adsorbed on the Pd surface are also reported, and dissociation pathways with smaller energy barriers than found for the ground state are shown to exist.

Theoretical Study of the Molecular and Electronic Structures of TiO4H4, Ti2O7H6, and Ti2O6H4

Takashi Tsuchiya and Jerry L. Whitten, J. Phys. Chem. C, 2011, 115 (5), pp 1635–1642

Abstract. State-of-the-art multi-state configuration interaction (CI) calculations are performed for a series of titanium oxygen complexes chosen to identify features present in titanium oxide nanoclusters and titanium dioxide surfaces. All electrons are included in the calculations and transformation methods are employed to achieve high accuracy for the excitations of interest. The electronic structures of the ground and excited states are discussed and excitation energies are reported for different molecular conformations. Of particular interest is the high degree of localization of the electron-hole pair formed on electronic excitation leading to a description of the lowest excited state as an O2p hole Ti 3d-electron exciton for all systems investigated. Singlet and triplet excited states are resolved and energies of electronic states are reported as a function of molecular geometry.

Configuration interaction study of the ground and excited states of TiO2 ring structures

Takashi Tsuchiya and Jerry L. Whitten, Journal of Chemical Physics, 134, 114701 (2011).

Abstract. Theoretical studies of the ground and lowest excited singlet and triplet states of a series of titanium dioxide ring structures, (TiO2)2n, n = 3–9, are reported. Calculations are based on many-electron configuration theory, where energies of states and geometrical structures are determined by variational energy minimization. The lowest energy excited states correspond to excitations from oxygen 2p levels to unoccupied 3d orbitals on titanium. For each ring system, two types of excited state solutions are investigated: those that maintain periodic symmetry for individual orbitals and solutions that allow the symmetry to be broken. The latter solutions which correspond to localized states or excitons are found to be significantly lower in energy than the symmetric solutions. We compare the vertical excitation energy of these well-defined geometrical structures with size effects reported in experimental studies.

Generation of Highly n-Type Titanium Oxide Using Plasma Fluorine Insertion

Hyungtak Seo, L. Robert Baker, Antoine Hervier, Jinwoo Kim, J. L. Whitten, and Gabor A. Somorji, Nano Lett., 2011, 11 (2), pp 751–756

Abstract. Titanium oxide is a widely used metal-oxide semiconductor; its uses include catalysts, solar cells, transparent transistors, chemical sensors, and catalytic hot electron convertors. [1-7] Titanium oxide is considered intrinsically n-type because of native oxygen (O) vacancy donors. [8] However, O vacancy doping induces the formation of defect states in the bandgap, and at high O vacancy concentrations, a suboxide band structure forms that results in metallic transport, pins the Fermi level, and limits the excitation energy of hot carriers by charge trapping. [9-11] Consequently, O vacancy doping is not ideal for many metal-oxide semiconductor applications. A technique for true n-type doping of titanium oxide without the formation of mid-gap defect states would improve the efficiency of many current charge-based devices and expand the use of transition metal oxides to new applications. Here we show that plasma-assisted fluorine insertion passivates intrinsic defect states and that fluorine acts as an extrinsic n-type donor in titanium oxide. This enabled us to modify the Fermi level and transport properties of titanium oxide outside the limits of O vacancy doping. The origin of fluorine-induced surface electronic structure modification is also identified by ab-initio theoretical calculation. This expands the utility of titanium oxide for applications requiring highly n-type, low defect semiconductors. Potential applications include resistive switching memory devices, thin film transistors, high-efficiency solar cells, and photo- and support-catalysts.