Ross Larsen - Academia.edu (original) (raw)

Papers by Ross Larsen

Research paper thumbnail of Predictors of Engagement in Training As a Pathway to Understanding Implementation of the Responsive Classroom Approach

Research paper thumbnail of The Responsive Classroom Approach Increases the Use of Standards-Based Mathematics Teaching Practices1

Research paper thumbnail of The influence of fidelity of implementation on teacher–student interaction quality in the context of a randomized controlled trial of the Responsive Classroom approach

Journal of School Psychology, 2013

R. A. (2013). Does the Responsive Classroom approach affect the use of standards-based mathematic... more R. A. (2013). Does the Responsive Classroom approach affect the use of standards-based mathematics teaching practices? Results from a randomized controlled trial.

Research paper thumbnail of National Council of Teachers of Mathematics 2012 Research Presession

Participants Data were collected from control schools participating in a three-year longitudinal ... more Participants Data were collected from control schools participating in a three-year longitudinal cluster randomized control trial of a socio-emotional learning intervention. Students and teachers from eleven schools in a large mid-Atlantic school district were studied. All third grade children (n= 205) who received free or reduced price lunch participated. They included 105 males; 108 Hispanic, 19 Caucasian, 43 African American, and 27 Asian American; 170 English Language Learners; and 30 students who received ...

Research paper thumbnail of Relations between mathematical knowledge for teaching, mathematics instructional quality, and student achievement in the context of the Responsive Classroom Approach

Society for Research on Educational Effectiveness, 2011

Limit 4 pages single spaced.

Research paper thumbnail of Title: Relations between Mathematical Knowledge for Teaching, Mathematics Instructional Quality, and Student Achievement in the Context of the Responsive Classroom (RC) Approach

Research paper thumbnail of Factor Structure and Psychometrics of the Adolescent Health Risk Behavior Survey Instrument

American Journal of Health Behavior, 2010

To explore the factor structure and psychometric properties of data collected with the Adolescent... more To explore the factor structure and psychometric properties of data collected with the Adolescent Health Risk Behavior Survey (AHRBS) instrument. Measures of the AHRBS instrument were tested using statistical analyses to assess validity and reliability of data collected from a sample of 1992 Indiana adolescents. Factor analyses yielded a 13-factor solution with acceptable model fit statistics. Tests of internal consistency reliability for data in instrument scales ranged from 0.455 to 0.916. Measures were consistent across adolescent subdemographic categories. The AHRBS instrument is a valuable tool for investigating adolescent drug use.

Research paper thumbnail of Developmental trajectories of aggression, prosocial behavior, and social-cognitive problem solving in emerging adolescents with clinically elevated attention-deficit/hyperactivity disorder symptoms

Journal of abnormal psychology, 2015

Middle school is a critical yet understudied period of social behavioral risks and opportunities ... more Middle school is a critical yet understudied period of social behavioral risks and opportunities that may be particularly difficult for emerging adolescents with attention-deficit/hyperactivity disorder (ADHD) given their childhood social difficulties. Relatively few ADHD studies have examined social behavior and social-cognitive problem solving beyond the elementary years, or examined aspects of positive (prosocial) behavior. The current study examined how middle school students with clinically elevated ADHD symptoms differ from their non-ADHD peers on baseline (6th grade) and age-related changes in prosocial and aggressive behavior, and the extent to which social-cognitive problem solving strategies mediate these relations. Emerging adolescents with (n = 178) and without (n = 3,806) clinically elevated, teacher-reported ADHD-combined symptoms were compared longitudinally across 6th through 8th grades using parallel process latent growth curve modeling, accounting for student demog...

Research paper thumbnail of Unpacking intervention effects: Teacher responsiveness as a mediator of perceived intervention quality and change in teaching practice

Early Childhood Research Quarterly, 2016

Research paper thumbnail of How positive processes function in negative relationships: Dispositional gratitude moderates the association between affective need and frequency of dating violence victimization

The Journal of Positive Psychology, 2015

Research paper thumbnail of Understanding nonequilibrium solute and solvent motions through molecular projections: Computer simulations of solvation dynamics in liquid tetrahydrofuran (THF)

The Journal of Physical Chemistry B, Dec 1, 2003

In this paper, we investigate the solvation dynamics of the weakly polar organic solvent tetrahyd... more In this paper, we investigate the solvation dynamics of the weakly polar organic solvent tetrahydrofuran (THF) via classical molecular dynamics simulation. We find that the relaxation dynamics of all of the rotational and translational degrees of freedom of neat THF occur on similar time scales and have similar power spectra, making it impossible to use spectral density analysis to discern which specific molecular motions are involved in solvation. Instead, we probe the molecular origins of solvation dynamics using a nonequilibrium projection formalism that we originally outlined in M. J. Bedard-Hearn et al., J. Phys. Chem. A 2003, 107 (24), 4773. Here, we expand this formalism and use it to study the nonequilibrium solvation dynamics for a model reaction in THF in which a charge is removed from an anionic Lennard-Jones (LJ) solute, leaving behind a smaller neutral atom. The solute parameters are chosen to model the photodetachment of an electron from a sodium anion, Naf Na 0 , to compare to the results of ultrafast spectroscopic experiments of this reaction being performed in our lab. We are able to explain the hidden breakdown of linear response for this system that we uncovered in our previous work in terms of the dynamical properties of the neat liquid and the structural properties of the solutions. In particular, our nonequilibrium projection analysis shows that four distinct solvation mechanisms are operative: (1) a rapid relaxation (t e 700 fs) caused by longitudinal translational motions that dramatically change the local solvation structure; (2) a slower relaxation (t > 700 fs) caused by diffusive longitudinal translational motions that completes the transformation of the long-range solute-solvent packing;

Research paper thumbnail of Bidirectional associations between perceived parental support for violent and nonviolent responses and early adolescent aggressive and effective nonviolent behaviors

Journal of adolescence, Jan 15, 2015

The current study examined bidirectional relations between early adolescents' perceptions of ... more The current study examined bidirectional relations between early adolescents' perceptions of parental support for violent and nonviolent responses to conflict and their aggressive and effective nonviolent behaviors six months later. Data was collected across the sixth and seventh grades for 520 adolescents at three middle schools in the southeastern United States. At baseline, participants were ages 10-14 (M = 11.29). Longitudinal path models showed that perceived parental support for violent responses was negatively associated with effective nonviolent behaviors and positively associated with aggressive behaviors across sixth and seventh grades. Across seventh grade, reciprocal negative relations were found between perceived parental support of nonviolent responses and aggressive behaviors. Effective nonviolent behaviors were positively associated with perceived parental support for nonviolent responses. Study implications include the importance of adolescent perceptions of par...

Research paper thumbnail of Reading and spelling skills in German third graders: Examining the role of student and context characteristics

The British journal of educational psychology, Jan 10, 2015

Educational processes and outcomes are influenced by a multitude of factors, including individual... more Educational processes and outcomes are influenced by a multitude of factors, including individual and contextual characteristics. Recently, studies have demonstrated that student and context characteristics may produce unique and cumulative effects on educational outcomes. The study aimed to investigate (1) the relative contribution of student, classroom, and school characteristics to reading fluency and orthographic spelling, (2) the relative contribution of specific predictors to reading fluency and orthographic spelling within the sets of student, classroom, and school characteristics, and (3) whether the contribution of student, classroom, and school characteristics differs for reading fluency and orthographic spelling. Participants were 789 German third-grade students from 56 classrooms in 34 schools. Students completed an intelligence test and a questionnaire assessing self-control. Reading fluency and orthographic spelling performance were assessed using standardized achievem...

Research paper thumbnail of Close Packing of Nitroxide Radicals in Stable Organic Radical Polymeric Materials

The Journal of Physical Chemistry Letters, 2015

The relationship between the polymer network and electronic transport properties for stable radic... more The relationship between the polymer network and electronic transport properties for stable radical polymeric materials has come under investigation owing to their potential application in electronic devices. For the radical polymer poly(2,2,6,6-tetramethylpiperidine-4-yl-1-oxyl methacrylate), it is unclear whether the radical packing is optimal for charge transport partially because the relationship between radical packing and molecular structure is not well-understood. Using the paramagnetic nitroxide radical as a probe of the polymer and synthetic techniques to control the radical concentration on the methyl methacrylate backbone, we investigate the dependence of radical concentration on molecular structure. The electron paramagnetic resonance data indicate that radicals in the PTMA assume a closest approach distance to each other when more than 60% of the backbone is populated with radical pendant groups. Below 60% coverage, the polymer rearranges to accommodate larger radical-radical spacing. These findings are consistent with theoretical calculations and help explain some experimentally determined electron-transport properties.

Research paper thumbnail of Triphenylamine-based star-shaped absorbers with tunable energy levels for organic photovoltaics

2010 35th IEEE Photovoltaic Specialists Conference, 2010

A new family of soluble low-bandgap star-shaped molecules based upon triphenylamine (TPA) and con... more A new family of soluble low-bandgap star-shaped molecules based upon triphenylamine (TPA) and containing benzothiadiazole (BTD) acceptor moieties have been designed and synthesized for organic photovoltaic (OPV) applications. The design results in the lowest unoccupied molecular orbital (LUMO) being spatially distributed on the periphery of the molecule, allowing facile photo-induced electron transfer to the fullerene phenyl C61 butyric acid methyl ester (PCBM). Photoluminescence quenching studies indicate efficient quenching of excitons, while time-resolved microwave conductivity experiments demonstrate effective separation of charges. Adjunct electron-withdrawing moieties allow tuning of the LUMO level. Theoretical calculations indicate three derivatives with LUMO levels in varying proximity to that of PCBM, which allows empirical testing of the theorized need for a 0.3 eV LUMO offset to ensure efficient charge transfer to PCBM. Design, characterization and bulk heterojunction device results for the new materials will be presented.

Research paper thumbnail of Oligomeric dithienopyrrole-thienopyrroledione (DTP-TPD) donor-acceptor copolymer for organic photovoltaics

2011 37th IEEE Photovoltaic Specialists Conference, 2011

Research paper thumbnail of Exploring the Role of Decoherence in Condensed-Phase Nonadiabatic Dynamics:  A Comparison of Different Mixed Quantum/Classical Simulation Algorithms for the Excited Hydrated Electron

The Journal of Physical Chemistry B, 2006

Mixed quantum/classical (MQC) molecular dynamics simulation has become the method of choice for s... more Mixed quantum/classical (MQC) molecular dynamics simulation has become the method of choice for simulating the dynamics of quantum mechanical objects that interact with condensed-phase systems. There are many MQC algorithms available, however, and in cases where nonadiabatic coupling is important, different algorithms may lead to different results. Thus, it has been difficult to reach definitive conclusions about relaxation dynamics using nonadiabatic MQC methods because one is never certain whether any given algorithm includes enough of the necessary physics. In this paper, we explore the physics underlying different nonadiabatic MQC algorithms by comparing and contrasting the excited-state relaxation dynamics of the prototypical condensed-phase MQC system, the hydrated electron, calculated using different algorithms, including: fewest-switches surface hopping, stationary-phase surface hopping, and mean-field dynamics with surface hopping. We also describe in detail how a new nonadiabatic algorithm, mean-field dynamics with stochastic decoherence (MF-SD), is to be implemented for condensed-phase problems, and we apply MF-SD to the excited-state relaxation of the hydrated electron. Our discussion emphasizes the different ways quantum decoherence is treated in each algorithm and the resulting implications for hydrated-electron relaxation dynamics. We find that for three MQC methods that use Tully's fewest-switches criterion to determine surface hopping probabilities, the excited-state lifetime of the electron is the same. Moreover, the nonequilibrium solvent response function of the excited hydrated electron is the same with all of the nonadiabatic MQC algorithms discussed here, so that all of the algorithms would produce similar agreement with experiment. Despite the identical solvent response predicted by each MQC algorithm, we find that MF-SD allows much more mixing of multiple basis states into the quantum wave function than do other methods. This leads to an excited-state lifetime that is longer with MF-SD than with any method that incorporates nonadiabatic effects with the fewest-switches surface hopping criterion.

Research paper thumbnail of Hidden Breakdown of Linear Response:  Projections of Molecular Motions in Nonequilibrium Simulations of Solvation Dynamics

The Journal of Physical Chemistry A, 2003

Research paper thumbnail of Resonance Raman and temperature-dependent electronic absorption spectra of cavity and noncavity models of the hydrated electron

Proceedings of the National Academy of Sciences, 2013

Most of what is known about the structure of the hydrated electron comes from mixed quantum/class... more Most of what is known about the structure of the hydrated electron comes from mixed quantum/classical simulations, which depend on the pseudopotential that couples the quantum electron to the classical water molecules. These potentials usually are highly repulsive, producing cavity-bound hydrated electrons that break the local water H-bonding structure. However, we recently developed a more attractive potential, which produces a hydrated electron that encompasses a region of enhanced water density. Both our noncavity and the various cavity models predict similar experimental observables. In this paper, we work to distinguish between these models by studying both the temperature dependence of the optical absorption spectrum, which provides insight into the balance of the attractive and repulsive terms in the potential, and the resonance Raman spectrum, which provides a direct measure of the local H-bonding environment near the electron. We find that only our noncavity model can capture the experimental red shift of the hydrated electron's absorption spectrum with increasing temperature at constant density. Cavity models of the hydrated electron predict a solvation structure similar to that of the larger aqueous halides, leading to a Raman O-H stretching band that is blue-shifted and narrower than that of bulk water. In contrast, experiments show the hydrated electron has a broader and red-shifted O-H stretching band compared with bulk water, a feature recovered by our noncavity model. We conclude that although our noncavity model does not provide perfect quantitative agreement with experiment, the hydrated electron must have a significant degree of noncavity character.

Research paper thumbnail of Projections of Quantum Observables onto Classical Degrees of Freedom in Mixed Quantum-Classical Simulations: Understanding Linear Response Failure for the Photoexcited Hydrated Electron

Physical Review Letters, 2006

We present a general analytic method for understanding how specific motions of a classical bath i... more We present a general analytic method for understanding how specific motions of a classical bath influence the dynamics of quantum-mechanical observables in mixed quantum-classical molecular dynamics simulations. We apply our method and develop expressions for the special case of quantum solvation, allowing us to examine how specific classical solvent motions couple to the equilibrium energy fluctuations and nonequilibrium energy relaxation of a quantum-mechanical solute. As a first application of our formalism, we investigate the motions of classical water underlying the equilibrium and nonequilibrium excited-state solvent response functions of the hydrated electron; the results allow us to explain why the linear response approximation fails for this system.

Research paper thumbnail of Predictors of Engagement in Training As a Pathway to Understanding Implementation of the Responsive Classroom Approach

Research paper thumbnail of The Responsive Classroom Approach Increases the Use of Standards-Based Mathematics Teaching Practices1

Research paper thumbnail of The influence of fidelity of implementation on teacher–student interaction quality in the context of a randomized controlled trial of the Responsive Classroom approach

Journal of School Psychology, 2013

R. A. (2013). Does the Responsive Classroom approach affect the use of standards-based mathematic... more R. A. (2013). Does the Responsive Classroom approach affect the use of standards-based mathematics teaching practices? Results from a randomized controlled trial.

Research paper thumbnail of National Council of Teachers of Mathematics 2012 Research Presession

Participants Data were collected from control schools participating in a three-year longitudinal ... more Participants Data were collected from control schools participating in a three-year longitudinal cluster randomized control trial of a socio-emotional learning intervention. Students and teachers from eleven schools in a large mid-Atlantic school district were studied. All third grade children (n= 205) who received free or reduced price lunch participated. They included 105 males; 108 Hispanic, 19 Caucasian, 43 African American, and 27 Asian American; 170 English Language Learners; and 30 students who received ...

Research paper thumbnail of Relations between mathematical knowledge for teaching, mathematics instructional quality, and student achievement in the context of the Responsive Classroom Approach

Society for Research on Educational Effectiveness, 2011

Limit 4 pages single spaced.

Research paper thumbnail of Title: Relations between Mathematical Knowledge for Teaching, Mathematics Instructional Quality, and Student Achievement in the Context of the Responsive Classroom (RC) Approach

Research paper thumbnail of Factor Structure and Psychometrics of the Adolescent Health Risk Behavior Survey Instrument

American Journal of Health Behavior, 2010

To explore the factor structure and psychometric properties of data collected with the Adolescent... more To explore the factor structure and psychometric properties of data collected with the Adolescent Health Risk Behavior Survey (AHRBS) instrument. Measures of the AHRBS instrument were tested using statistical analyses to assess validity and reliability of data collected from a sample of 1992 Indiana adolescents. Factor analyses yielded a 13-factor solution with acceptable model fit statistics. Tests of internal consistency reliability for data in instrument scales ranged from 0.455 to 0.916. Measures were consistent across adolescent subdemographic categories. The AHRBS instrument is a valuable tool for investigating adolescent drug use.

Research paper thumbnail of Developmental trajectories of aggression, prosocial behavior, and social-cognitive problem solving in emerging adolescents with clinically elevated attention-deficit/hyperactivity disorder symptoms

Journal of abnormal psychology, 2015

Middle school is a critical yet understudied period of social behavioral risks and opportunities ... more Middle school is a critical yet understudied period of social behavioral risks and opportunities that may be particularly difficult for emerging adolescents with attention-deficit/hyperactivity disorder (ADHD) given their childhood social difficulties. Relatively few ADHD studies have examined social behavior and social-cognitive problem solving beyond the elementary years, or examined aspects of positive (prosocial) behavior. The current study examined how middle school students with clinically elevated ADHD symptoms differ from their non-ADHD peers on baseline (6th grade) and age-related changes in prosocial and aggressive behavior, and the extent to which social-cognitive problem solving strategies mediate these relations. Emerging adolescents with (n = 178) and without (n = 3,806) clinically elevated, teacher-reported ADHD-combined symptoms were compared longitudinally across 6th through 8th grades using parallel process latent growth curve modeling, accounting for student demog...

Research paper thumbnail of Unpacking intervention effects: Teacher responsiveness as a mediator of perceived intervention quality and change in teaching practice

Early Childhood Research Quarterly, 2016

Research paper thumbnail of How positive processes function in negative relationships: Dispositional gratitude moderates the association between affective need and frequency of dating violence victimization

The Journal of Positive Psychology, 2015

Research paper thumbnail of Understanding nonequilibrium solute and solvent motions through molecular projections: Computer simulations of solvation dynamics in liquid tetrahydrofuran (THF)

The Journal of Physical Chemistry B, Dec 1, 2003

In this paper, we investigate the solvation dynamics of the weakly polar organic solvent tetrahyd... more In this paper, we investigate the solvation dynamics of the weakly polar organic solvent tetrahydrofuran (THF) via classical molecular dynamics simulation. We find that the relaxation dynamics of all of the rotational and translational degrees of freedom of neat THF occur on similar time scales and have similar power spectra, making it impossible to use spectral density analysis to discern which specific molecular motions are involved in solvation. Instead, we probe the molecular origins of solvation dynamics using a nonequilibrium projection formalism that we originally outlined in M. J. Bedard-Hearn et al., J. Phys. Chem. A 2003, 107 (24), 4773. Here, we expand this formalism and use it to study the nonequilibrium solvation dynamics for a model reaction in THF in which a charge is removed from an anionic Lennard-Jones (LJ) solute, leaving behind a smaller neutral atom. The solute parameters are chosen to model the photodetachment of an electron from a sodium anion, Naf Na 0 , to compare to the results of ultrafast spectroscopic experiments of this reaction being performed in our lab. We are able to explain the hidden breakdown of linear response for this system that we uncovered in our previous work in terms of the dynamical properties of the neat liquid and the structural properties of the solutions. In particular, our nonequilibrium projection analysis shows that four distinct solvation mechanisms are operative: (1) a rapid relaxation (t e 700 fs) caused by longitudinal translational motions that dramatically change the local solvation structure; (2) a slower relaxation (t > 700 fs) caused by diffusive longitudinal translational motions that completes the transformation of the long-range solute-solvent packing;

Research paper thumbnail of Bidirectional associations between perceived parental support for violent and nonviolent responses and early adolescent aggressive and effective nonviolent behaviors

Journal of adolescence, Jan 15, 2015

The current study examined bidirectional relations between early adolescents' perceptions of ... more The current study examined bidirectional relations between early adolescents' perceptions of parental support for violent and nonviolent responses to conflict and their aggressive and effective nonviolent behaviors six months later. Data was collected across the sixth and seventh grades for 520 adolescents at three middle schools in the southeastern United States. At baseline, participants were ages 10-14 (M = 11.29). Longitudinal path models showed that perceived parental support for violent responses was negatively associated with effective nonviolent behaviors and positively associated with aggressive behaviors across sixth and seventh grades. Across seventh grade, reciprocal negative relations were found between perceived parental support of nonviolent responses and aggressive behaviors. Effective nonviolent behaviors were positively associated with perceived parental support for nonviolent responses. Study implications include the importance of adolescent perceptions of par...

Research paper thumbnail of Reading and spelling skills in German third graders: Examining the role of student and context characteristics

The British journal of educational psychology, Jan 10, 2015

Educational processes and outcomes are influenced by a multitude of factors, including individual... more Educational processes and outcomes are influenced by a multitude of factors, including individual and contextual characteristics. Recently, studies have demonstrated that student and context characteristics may produce unique and cumulative effects on educational outcomes. The study aimed to investigate (1) the relative contribution of student, classroom, and school characteristics to reading fluency and orthographic spelling, (2) the relative contribution of specific predictors to reading fluency and orthographic spelling within the sets of student, classroom, and school characteristics, and (3) whether the contribution of student, classroom, and school characteristics differs for reading fluency and orthographic spelling. Participants were 789 German third-grade students from 56 classrooms in 34 schools. Students completed an intelligence test and a questionnaire assessing self-control. Reading fluency and orthographic spelling performance were assessed using standardized achievem...

Research paper thumbnail of Close Packing of Nitroxide Radicals in Stable Organic Radical Polymeric Materials

The Journal of Physical Chemistry Letters, 2015

The relationship between the polymer network and electronic transport properties for stable radic... more The relationship between the polymer network and electronic transport properties for stable radical polymeric materials has come under investigation owing to their potential application in electronic devices. For the radical polymer poly(2,2,6,6-tetramethylpiperidine-4-yl-1-oxyl methacrylate), it is unclear whether the radical packing is optimal for charge transport partially because the relationship between radical packing and molecular structure is not well-understood. Using the paramagnetic nitroxide radical as a probe of the polymer and synthetic techniques to control the radical concentration on the methyl methacrylate backbone, we investigate the dependence of radical concentration on molecular structure. The electron paramagnetic resonance data indicate that radicals in the PTMA assume a closest approach distance to each other when more than 60% of the backbone is populated with radical pendant groups. Below 60% coverage, the polymer rearranges to accommodate larger radical-radical spacing. These findings are consistent with theoretical calculations and help explain some experimentally determined electron-transport properties.

Research paper thumbnail of Triphenylamine-based star-shaped absorbers with tunable energy levels for organic photovoltaics

2010 35th IEEE Photovoltaic Specialists Conference, 2010

A new family of soluble low-bandgap star-shaped molecules based upon triphenylamine (TPA) and con... more A new family of soluble low-bandgap star-shaped molecules based upon triphenylamine (TPA) and containing benzothiadiazole (BTD) acceptor moieties have been designed and synthesized for organic photovoltaic (OPV) applications. The design results in the lowest unoccupied molecular orbital (LUMO) being spatially distributed on the periphery of the molecule, allowing facile photo-induced electron transfer to the fullerene phenyl C61 butyric acid methyl ester (PCBM). Photoluminescence quenching studies indicate efficient quenching of excitons, while time-resolved microwave conductivity experiments demonstrate effective separation of charges. Adjunct electron-withdrawing moieties allow tuning of the LUMO level. Theoretical calculations indicate three derivatives with LUMO levels in varying proximity to that of PCBM, which allows empirical testing of the theorized need for a 0.3 eV LUMO offset to ensure efficient charge transfer to PCBM. Design, characterization and bulk heterojunction device results for the new materials will be presented.

Research paper thumbnail of Oligomeric dithienopyrrole-thienopyrroledione (DTP-TPD) donor-acceptor copolymer for organic photovoltaics

2011 37th IEEE Photovoltaic Specialists Conference, 2011

Research paper thumbnail of Exploring the Role of Decoherence in Condensed-Phase Nonadiabatic Dynamics:  A Comparison of Different Mixed Quantum/Classical Simulation Algorithms for the Excited Hydrated Electron

The Journal of Physical Chemistry B, 2006

Mixed quantum/classical (MQC) molecular dynamics simulation has become the method of choice for s... more Mixed quantum/classical (MQC) molecular dynamics simulation has become the method of choice for simulating the dynamics of quantum mechanical objects that interact with condensed-phase systems. There are many MQC algorithms available, however, and in cases where nonadiabatic coupling is important, different algorithms may lead to different results. Thus, it has been difficult to reach definitive conclusions about relaxation dynamics using nonadiabatic MQC methods because one is never certain whether any given algorithm includes enough of the necessary physics. In this paper, we explore the physics underlying different nonadiabatic MQC algorithms by comparing and contrasting the excited-state relaxation dynamics of the prototypical condensed-phase MQC system, the hydrated electron, calculated using different algorithms, including: fewest-switches surface hopping, stationary-phase surface hopping, and mean-field dynamics with surface hopping. We also describe in detail how a new nonadiabatic algorithm, mean-field dynamics with stochastic decoherence (MF-SD), is to be implemented for condensed-phase problems, and we apply MF-SD to the excited-state relaxation of the hydrated electron. Our discussion emphasizes the different ways quantum decoherence is treated in each algorithm and the resulting implications for hydrated-electron relaxation dynamics. We find that for three MQC methods that use Tully's fewest-switches criterion to determine surface hopping probabilities, the excited-state lifetime of the electron is the same. Moreover, the nonequilibrium solvent response function of the excited hydrated electron is the same with all of the nonadiabatic MQC algorithms discussed here, so that all of the algorithms would produce similar agreement with experiment. Despite the identical solvent response predicted by each MQC algorithm, we find that MF-SD allows much more mixing of multiple basis states into the quantum wave function than do other methods. This leads to an excited-state lifetime that is longer with MF-SD than with any method that incorporates nonadiabatic effects with the fewest-switches surface hopping criterion.

Research paper thumbnail of Hidden Breakdown of Linear Response:  Projections of Molecular Motions in Nonequilibrium Simulations of Solvation Dynamics

The Journal of Physical Chemistry A, 2003

Research paper thumbnail of Resonance Raman and temperature-dependent electronic absorption spectra of cavity and noncavity models of the hydrated electron

Proceedings of the National Academy of Sciences, 2013

Most of what is known about the structure of the hydrated electron comes from mixed quantum/class... more Most of what is known about the structure of the hydrated electron comes from mixed quantum/classical simulations, which depend on the pseudopotential that couples the quantum electron to the classical water molecules. These potentials usually are highly repulsive, producing cavity-bound hydrated electrons that break the local water H-bonding structure. However, we recently developed a more attractive potential, which produces a hydrated electron that encompasses a region of enhanced water density. Both our noncavity and the various cavity models predict similar experimental observables. In this paper, we work to distinguish between these models by studying both the temperature dependence of the optical absorption spectrum, which provides insight into the balance of the attractive and repulsive terms in the potential, and the resonance Raman spectrum, which provides a direct measure of the local H-bonding environment near the electron. We find that only our noncavity model can capture the experimental red shift of the hydrated electron's absorption spectrum with increasing temperature at constant density. Cavity models of the hydrated electron predict a solvation structure similar to that of the larger aqueous halides, leading to a Raman O-H stretching band that is blue-shifted and narrower than that of bulk water. In contrast, experiments show the hydrated electron has a broader and red-shifted O-H stretching band compared with bulk water, a feature recovered by our noncavity model. We conclude that although our noncavity model does not provide perfect quantitative agreement with experiment, the hydrated electron must have a significant degree of noncavity character.

Research paper thumbnail of Projections of Quantum Observables onto Classical Degrees of Freedom in Mixed Quantum-Classical Simulations: Understanding Linear Response Failure for the Photoexcited Hydrated Electron

Physical Review Letters, 2006

We present a general analytic method for understanding how specific motions of a classical bath i... more We present a general analytic method for understanding how specific motions of a classical bath influence the dynamics of quantum-mechanical observables in mixed quantum-classical molecular dynamics simulations. We apply our method and develop expressions for the special case of quantum solvation, allowing us to examine how specific classical solvent motions couple to the equilibrium energy fluctuations and nonequilibrium energy relaxation of a quantum-mechanical solute. As a first application of our formalism, we investigate the motions of classical water underlying the equilibrium and nonequilibrium excited-state solvent response functions of the hydrated electron; the results allow us to explain why the linear response approximation fails for this system.