Imperial College London

ProfessorMichaelBearpark

Faculty of Natural SciencesDepartment of Chemistry

Professor & Director of User Engagement
 
 
 
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Contact

 

+44 (0)20 7594 5727m.bearpark

 
 
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Location

 

110AMolecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

151 results found

Danilov D, Jenkins AJ, Bearpark MJ, Worth GA, Robb MAet al., 2023, Coherent mixing of singlet and triplet states in acrolein and ketene: a computational strategy for simulating the electron-nuclear dynamics of intersystem crossing., Journal of Physical Chemistry Letters, Vol: 14, Pages: 6127-6134, ISSN: 1948-7185

We present a theoretical study of intersystem crossing (ISC) in acrolein and ketene with the Ehrenfest method that can describe a superposition of singlet and triplet states. Our simulations illustrate a new mechanistic effect of ISC, namely, that a superposition of singlets and triplets yields nonadiabatic dynamics characteristic of that superposition rather than the constituent state potential energy surfaces. This effect is particularly significant in ketene, where mixing of singlet and triplet states along the approach to a singlet/singlet conical intersection occurs, with the spin-orbit coupling (SOC) remaining small throughout. In both cases, the effects require many recrossings of the singlet/triplet state crossing seam, consistent with the textbook treatment of ISC.

Journal article

Segarra-Marti J, Tran T, Bearpark MJ, 2022, 3-Methylation alters excited state decay in photoionised uracil, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 24, Pages: 27038-27046, ISSN: 1463-9076

Journal article

Danilov D, Tran T, Bearpark MJJ, Marangos JPP, Worth GAA, Robb MAAet al., 2022, How electronic superpositions drive nuclear motion following the creation of a localized hole in the glycine radical cation, JOURNAL OF CHEMICAL PHYSICS, Vol: 156, ISSN: 0021-9606

Journal article

Cave-Ayland C, Bearpark M, Romain C, Rzepa Het al., 2022, CHAMP is a HPC Access and Metadata Portal, Journal of Open Source Software, Vol: 7, Pages: 3824-3824

Journal article

Chan HHS, Fitzpatrick N, Segarra-Marti J, Bearpark MJ, Tew DPet al., 2021, Molecular excited state calculations with adaptive wavefunctions on a quantum eigensolver emulation: reducing circuit depth and separating spin states, Physical Chemistry Chemical Physics, Vol: 23, Pages: 26438-26450, ISSN: 1463-9076

Ab initio electronic excited state calculations are necessary for the quantitative study of photochemical reactions, but their accurate computation on classical computers is plagued by prohibitive resource scaling. The Variational Quantum Deflation (VQD) is an extension of the quantum-classical Variational Quantum Eigensolver (VQE) algorithm for calculating electronic excited state energies, and has the potential to address some of these scaling challenges using quantum computers. However, quantum computers available in the near term can only support a limited number of quantum circuit operations, so reducing the quantum computational cost in VQD methods is critical to their realisation. In this work, we investigate the use of adaptive quantum circuit growth (ADAPT-VQE) in excited state VQD calculations, a strategy that has been successful previously in reducing the resources required for ground state energy VQE calculations. We also invoke spin restrictions to separate the recovery of eigenstates with different spin symmetry to reduce the number of calculations and accumulation of errors in computing excited states. We created a quantum eigensolver emulation package - Quantum Eigensolver Building on Achievements of Both quantum computing and quantum chemistry (QEBAB) – for testing the proposed adaptive procedure against two existing VQD methods that use fixed-length quantum circuits: UCCGSD-VQD and k-UpCCGSD-VQD. For a lithium hydride test case we found that the spin-restricted adaptive growth variant of VQD uses the most compact circuits out of the tested methods by far, consistently recovers adequate electron correlation energy for different nuclear geometries and eigenstates while isolating the singlet and triplet manifold. This work is a further step towards developing techniques which improve the efficiency of hybrid quantum algorithms for excited state quantum chemistry, opening up the possibility of exploiting real quantum computers for electronic exci

Journal article

Segarra-Martí J, Bearpark MJ, 2021, Modelling photoionisation in isocytosine: potential formation of longer-lived excited state cations in its keto form., ChemPhysChem: a European journal of chemical physics and physical chemistry, Vol: 22, Pages: 2172-2181, ISSN: 1439-4235

Studying the effects of UV and VUV radiation on non-canonical DNA/RNA nucleobases allows us to compare how they release excess energy following absorption with respect to their canonical counterparts. This has attracted much research attention in recent years because of its likely influence on the origin of our genetic lexicon in prebiotic times. Here we present a CASSCF and XMS-CASPT2 theoretical study of the photoionisation of non-canonical pyrimidine nucleobase isocytosine in both its keto and enol tautomeric forms. We analyse their lowest energy cationic excited states including 2 π + , 2 n O +  and 2 n N +  and compare these to the corresponding electronic states in cytosine. Investigating lower-energy decay pathways we find - unexpectedly - that keto-isocytosine + presents a sizeable energy barrier potentially inhibiting decay to its cationic ground state, whereas enol-isocytosine + features a barrierless and consequently ultrafast pathway analogous to the one previously found for the canonical (keto) form of cytosine + . Dynamic electron correlation reduces the energy barrier in the keto form substantially (by ~1 eV) but it is nevertheless still present. We additionally compute UV/Vis absorption signals of the structures encountered along these decay channels to provide spectroscopic fingerprints to assist future experiments in monitoring these intricate photo-processes.

Journal article

Segarra-Martí J, Bearpark MJ, 2021, Modelling Photoionisation in Isocytosine: Potential Formation of Longer-Lived Excited State Cations in its Keto Form., Chemphyschem, Vol: 22

The front cover artwork is provided by Dr. Javier Segarra-Martí (University of Valencia, Spain) and Prof. Michael J. Bearpark (Imperial College London, UK). The image shows the ultrafast photoionisation of DNA canonical nucleobase cytosine and the slower ionization process in non-canonical base isocytosine embedded within a DNA backbone. Read the full text of the Article at 10.1002/cphc.202100402.

Journal article

Segarra-Martí J, Nouri SM, Bearpark MJ, 2021, Modelling photoionisations in tautomeric DNA nucleobase derivatives 7H-adenine and 7H-Guanine: ultrafast decay and photostability, Photochem, Vol: 1, Pages: 287-301, ISSN: 2673-7256

The study of radiation effects in DNA is a multidisciplinary endeavour, connecting the physical, chemical and biological sciences. Despite being mostly filtered by the ozone layer, sunlight radiation is still expected to (photo)ionise DNA in sizeable yields, triggering an electron removal process and the formation of potentially reactive cationic species. In this manuscript, photoionisation decay channels of important DNA tautomeric derivatives, 7H-adenine and 7H-guanine, are characterised with accurate CASSCF/XMS-CASPT2 theoretical methods. These simulation techniques place the onset of ionisation for 7H-adenine and 7H-guanine on average at 8.98 and 8.43 eV, in line with recorded experimental evidence when available. Cationic excited state decays are analysed next, uncovering effective barrierless deactivation routes for both species that are expected to decay to their (cationic) ground state on ultrafast timescales. Conical intersection topographies reveal that these photoionisation processes are facilitated by sloped single-path crossings, known to foster photostability, and which are predicted to enable the (VUV) photo-protection mechanisms present in these DNA tautomeric species.

Journal article

Barillot T, Alexander O, Cooper B, Driver T, Garratt D, Li S, Al Haddad A, Sanchez-Gonzalez A, Agåker M, Arrell C, Bearpark MJ, Berrah N, Bostedt C, Bozek J, Brahms C, Bucksbaum PH, Clark A, Doumy G, Feifel R, Frasinski LJ, Jarosch S, Johnson AS, Kjellsson L, Kolorenč P, Kumagai Y, Larsen EW, Matia-Hernando P, Robb M, Rubensson J-E, Ruberti M, Sathe C, Squibb RJ, Tan A, Tisch JWG, Vacher M, Walke DJ, Wolf TJA, Wood D, Zhaunerchyk V, Walter P, Osipov T, Marinelli A, Maxwell TJ, Coffee R, Lutman AA, Averbukh V, Ueda K, Cryan JP, Marangos JPet al., 2021, Correlation-driven transient hole dynamics resolved in space and time in the isopropanol molecule, Physical Review X, Vol: 11, Pages: 1-15, ISSN: 2160-3308

The possibility of suddenly ionized molecules undergoing extremely fast electron hole (or, hole)dynamics prior to significant structural change was first recognized more than 20 years ago andtermed charge migration. The accurate probing of ultrafast electron hole dynamics requires measurements that have both sufficient temporal resolution and can detect the localization of a specifichole within the molecule. We report an investigation of the dynamics of inner valence hole states inisopropanol where we use an x-ray pump/x-ray probe experiment, with site and state-specific probing of a transient hole state localized near the oxygen atom in the molecule, together with an abinitio theoretical treatment. We record the signature of transient hole dynamics and make the firsttentative observation of dynamics driven by frustrated Auger-Meitner transitions. We verify thatthe effective hole lifetime is consistent with our theoretical prediction. This state-specific measurement paves the way to widespread application for observations of transient hole dynamics localizedin space and time in molecules and thus to charge transfer phenomena that are fundamental inchemical and material physics.

Journal article

Fare C, Yuan L, Cordon-Preciado V, Michels JJ, Bearpark MJ, Rich PR, van Thor JJet al., 2020, A radical-triggered reaction mechanism of the green-to-red photoconversion of EosFP, The Journal of Physical Chemistry B, Vol: 124, Pages: 7765-7778, ISSN: 1520-6106

Reaction intermediates in the green-to-red photoconversion of the photochromic fluorescent protein EosFP have been observed using high-intensity continuous blue illumination. An intermediate was identified through light induced accumulation that continues to convert the green form in subsequent darkness, putatively containing a tyrosyl radical, albeit with anomalously shifted features in both electronic and FTIR spectra. Lowering the pH to 5.5 significantly delays the decay of this tyrosyl intermediate, which is accompanied by Stark-shifted features in the electronic spectra of reactants and products. Vibrational mode assignments for the high frequency and fingerprint FTIR spectral regions of reaction intermediates support a proposed sequence of events where the newly formed Cα=Cβ ethylenic bond precedes modifications on the His62 imidazole ring and confirms a C=O(NH2) product group on Phe61. We propose a reaction mechanism that involves tyrosyl generation via singlet excited state mediated oxidation which subsequently triggers the covalent reactions by oxidation of the green chromophore.

Journal article

Segarra-Martí J, Segatta F, Mackenzie TA, Nenov A, Rivalta I, Bearpark M, Garavelli Met al., 2020, Modeling multidimensional spectral lineshapes from first principles: Application to water-solvated adenine, Faraday Discussions, Vol: 221, Pages: 219-244, ISSN: 1359-6640

In this discussion we present a methodology to describe spectral lineshape from first principles, providing insight into the solvent-solute molecular interactions in terms of static and dynamic disorder and how these shape the signals recorded experimentally in linear and nonlinear optical spectroscopies, including two-dimensional electronic spectroscopy (2DES). Two different strategies for simulating the lineshape are compared, in which both the coupling to the intra-molecular vibrations and the influence exerted by the different water distributions attained along a molecular dynamics (MD) simulation are accurately described. The first method accounts for such water arrangements as first order perturbations on the adenine energies computed for a single reference (gas phase) quantum calculation. The second method requires to compute the manifold of excited states explicitly at each simulation snapshot, employing a hybrid quantum mechanics/molecular mechanics (QM/MM) scheme. Both approaches are applied to a large number of states of the adenine singlet excited manifold (chosen because of its biological role), and compared with available experimental data. They give comparable results but the first approach is two orders of magnitude faster. We show how the various contributions (static/dynamic disorder, intra-/inter-molecular interactions) sum up to build the total broadening observed in experiments.

Journal article

Segarra-Marti J, Tran T, Bearpark M, 2019, Computing the ultrafast and radiationless electronic excited state decay of cytosine and 5‐methyl‐cytosine cations: uncovering the role of dynamic electron correlation, ChemPhotoChem, Vol: 3, Pages: 856-865, ISSN: 2367-0932

Photoionisation in DNA, i.e. the process of photoinduced electron removal from the chromophoric species − the nucleobases − leading to their cationic form, has been scarcely studied despite being considered to be responsible for significant damaging instances in our genetic material. In this contribution we theoretically characterise the electronic ground and excited state decay pathways of cationic DNA nucleobase cytosine+ and its epigenetic derivative 5‐methyl‐cytosine+, including the effects of dynamic electron correlation on energies and geometries of minima and conical intersections. We do this by comparing the results of XMS‐CASPT2 calculations with CASSCF estimates and we find some significant differences between the results of these two methods. In particular, including dynamic electron correlation is found to significantly reduce the barrier to access the (D1/D0) conical intersection. We find notable similarities in both cytosine and 5‐methyl‐cytosine cations, accessible conical intersections in the vicinity of the Franck‐Condon region are found. This points towards an ultrafast depopulation of their electronic excited states. Moreover, the shape of the ground state potential energy surface strongly directs the decaying excited state population towards the cationic ground state minimum on ultrafast timescales, preventing photofragmentation and thus explaining their photostability.

Journal article

Tran T, Segarra-Martí J, Bearpark M, Robb MAet al., 2019, Molecular vertical excitation energies studied with first-order RASSCF (RAS[1,1]): balancing covalent and ionic excited states, Journal of Physical Chemistry A, Vol: 123, Pages: 5223-5230, ISSN: 1089-5639

RASSCF calculations of vertical excitation energies were carried out on a benchmark set of 19 organic molecules studied by Thiel and co-workers [ J. Chem. Phys. 2008, 128, 134110]. The best results, in comparison with the MS-CASPT2 results of Thiel, were obtained using a RASSCF space that contains at most one hole and one particle in the RAS1 and RAS3 spaces, respectively, which we denote as RAS[1,1]. This subset of configurations recovers mainly the effect of polarization and semi-internal electronic correlation that is only included in CASSCF in an averaged way. Adding all-external correlation by allowing double excitations from RAS1 and RAS2 into RAS3 did not improve the results, and indeed, they were slightly worse. The accuracy of the first-order RASSCF computations is demonstrated to be a function of whether the state of interest can be classified as covalent or ionic in the space of configurations built from orbitals localized onto atomic sites. For covalent states, polarization and semi-internal correlation effects are negligible (RAS[1,1]), while for ionic states, these effects are large (because of inherent diffusiveness of these states compared to the covalent states) and, thus, an acceptable agreement with MS-CASPT2 can be obtained using first-order RASSCF with the extra basis set involving 3p orbitals in most cases. However, for those ionic states that are quasi-degenerate with a Rydberg state or for nonlocal nπ* states, there remains a significant error resulting from all external correlation effects.

Journal article

Segarra-Martí J, Tran T, Bearpark MJ, 2019, Ultrafast and radiationless electronic excited state decay of uracil and thymine cations: computing the effects of dynamic electron correlation, Physical Chemistry Chemical Physics, Vol: 21, Pages: 14322-14330, ISSN: 1463-9076

In this article we characterise the radiationless decay of the first few electronic excited states of the cations of DNA/RNA nucleobases uracil and thymine, including the effects of dynamic electron correlation on energies and geometries (optimised with XMS-CASPT2). In both systems, we find that one state of 2n+O and another two of 2π+ character can be populated following photoionisation, and their different minima and interstate crossings are located. We find strong similarities between uracil and thymine cations: with accessible conical intersections suggesting that depopulation of their electronic excited states takes place on ultrafast timescales in both systems, suggesting that they are photostable in agreement with previous theoretical (uracil+) evidence. We find that dynamic electron correlation separates the energy levels of the "3-state" conical intersection (D2/D1/D0)CI previously located with CASSCF for uracil+, which will therefore have a different geometry and higher energy. Simulating the electronic and vibrational absorptions allows us to characterise spectral fingerprints that could be used to monitor these cation photo-processes experimentally.

Journal article

Polyak I, Bearpark MJ, Robb MA, 2018, Application of the unitary group approach (UGA) to evaluate spindensity for Configuration Interaction (CI) calculations in a basisof S$^{2}$ eigenfunctions, International Journal of Quantum Chemistry, Vol: 118, ISSN: 0020-7608

We present an implementation of the spin-dependent unitary group approachto calculate spin densities for CI calculations in a basis of spinsymmetry-adapted functions. Using S$^{2}$ eigenfunctions helps toreduce the size of configuration space and is beneficial in studiesof the systems where selection of states of specific spin symmetryis crucial. In order to achieve this, we combine the method to calculate$U(n)$ generator matrix elements developed by Robb and Downward~[\onlinecite{downward_1977}]with the approach of Gould and Battle to calculate $U(2n)$ generatormatrix elements~[\onlinecite{battle_1993}]. We also compareand contrast the spin density formulated in terms of the spin-independentunitary generators arising from the group theory formalism and equivalent formulation of the spin density representation in terms of the one- and two-electron charge densities.

Journal article

Polyak I, Jenkins A, Vacher M, Bouduban M, Bearpark M, Robb MAet al., 2018, Charge migration engineered by localisation: electron-nuclear dynamics in polyenes and glycine, Molecular Physics, Vol: 116, Pages: 2474-2489, ISSN: 0026-8976

We demonstrate that charge migration can be ‘engineered’ in arbitrary molecular systems if a single localised orbital – that diabatically follows nuclear displacements – is ionised. Specifically, we describe the use of natural bonding orbitals in Complete Active Space Configuration Interaction (CASCI) calculations to form cationic states with localised charge, providing consistently well-defined initial conditions across a zero point energy vibrational ensemble of molecular geometries. In Ehrenfest dynamics simulations following localised ionisation of -electrons in model polyenes (hexatriene and decapentaene) and -electrons in glycine, oscillatory charge migration can be observed for several femtoseconds before dephasing. Including nuclear motion leads to slower dephasing compared to fixed-geometry electron-only dynamics results. For future work, we discuss the possibility of designing laser pulses that would lead to charge migration that is experimentally observable, based on the proposed diabatic orbital approach.

Journal article

Vacher M, Bearpark M, Robb MA, Malhado JPet al., 2017, Electron dynamics upon ionisation of polyatomic molecules: Coupling to quantum nuclear motion and decoherence, Physical Review Letters, Vol: 118, Pages: 1-5, ISSN: 1079-7114

Knowledge about the electronic motion in molecules is essential for our understanding of chemicalreactions and biological processes. The advent of attosecond techniques opens up the possibility toinduce electronic motion, observe it in real time and potentially steer it. A fundamental questionremains the factors influencing electronic decoherence and the role played by nuclear motion in thisprocess. Here, we simulate the dynamics upon ionisation of the polyatomic molecules para-xyleneand modified bismethylene-adamantane, with a quantum mechanical treatment of both electron andnuclear dynamics using the direct dynamics variational multi-configuration Gaussian method. Oursimulations give new important physical insights about the expected decoherence process. We haveshown that the decoherence of electron dynamics happens on the time scale of a few femtoseconds,with the interplay of different mechanisms: thedephasingis responsible for the fast decoherencewhile thenuclear overlap decaymay actually help maintaining it and is responsible for small revivals.

Journal article

Spinlove KE, Vacher M, Bearpark M, Robb MA, Worth GAet al., 2017, Using quantum dynamics simulations to follow the competition between charge migration and charge transfer in polyatomic molecules, CHEMICAL PHYSICS, Vol: 482, Pages: 52-63, ISSN: 0301-0104

Journal article

Robb MA, 2016, Charge migration in polycyclic norbornadiene cations: winning the race against decoherence, Journal of Chemical Physics, Vol: 145, ISSN: 1089-7690

The observation of electronic motion remains a key target in the development of the eld of attoscience.However, systems in which long-lived oscillatory charge migration may be observed must be selected carefully,particularly because it has been shown that nuclear spatial delocalization leads to a loss of coherent electrondensity oscillations. Here we demonstrate electron dynamics in norbornadiene and extended systems wherethe hole density migrates between two identical chromophores. By studying the e ect of nuclear motionand delocalization in these example systems, we present the physical properties that must be considered incandidate molecules in which to observe electron dynamics. Furthermore, we also show a key contribution tonuclear delocalization arises from motion in the branching plane of the cation. For the systems studied, thedephasing time increases with system size while the energy gap between states, and therefore the frequency ofthe density oscillation, decreases with size (obeying a simple exponential dependence on the inter-chromophoredistance). We present a system that balances these two e ects and shows several complete oscillations in thespin density before dephasing occurs.

Journal article

Abdullahi MH, Thompson LM, Bearpark MJ, Vinader V, Afarinkia Ket al., 2016, The role of substituents in retro Diels-Alder extrusion of CO2 from 2(H)-pyrone cycloadducts, Tetrahedron, Vol: 72, Pages: 6021-6024, ISSN: 1464-5416

An experimental and computational investigation is conducted into the role of substituents in retro Diels–Alder extrusion of CO2 from 2-oxa-bicyclo[2.2.2]oct-5-en-3-ones. We provide the first experimental evidence that loss of CO2 from the cycloadducts significantly depends on the nature and position of the substituents. For example, we show that whilst 5-carboethoxy-2-pyrone undergoes a more facile cycloaddition that 3-carboethoxy-2-pyrone, the cycloadduct from the latter pyrone undergoes a more facile loss of CO2 than the cycloadduct from the former pyrone.

Journal article

Vacher M, Bearpark MJ, Robb MA, 2016, Direct methods for non-adiabatic dynamics: connecting the single-set variational multi-confguration Gaussian (vMCG) and Ehrenfest perspectives, Theoretical Chemistry Accounts, Vol: 135, ISSN: 1432-881X

In this article, we outline the current state-of-theart“on-the-fly” methods for non-adiabatic dynamics, highlightingthe similarities and differences between them. Wederive the equations of motion for both the Ehrenfest andvariational multi-configuration Gaussian (vMCG) methodsfrom the Dirac–Frenkel variational principle. We explorethe connections between these two methods by presentingan alternative derivation of the vMCG method, which givesthe Ehrenfest equations of motion when taking the appropriatelimits.

Journal article

Casellas J, Bearpark MJ, Reguero M, 2016, Excited-State Decay in the Photoisomerisation of Azobenzene: A New Balance between Mechanisms, Chemphyschem, Vol: 17, Pages: 3068-3079, ISSN: 1439-7641

The mechanism of the photoisomerization of azobenzene has been studied by means of multiconfigurational ab initio calculations. Our results show that it is necessary to account for the dynamic electron correlation in the location of the critical points (CASPT2 optimizations) to obtain a correct description of the topography of the potential energy surfaces of the low-energy singlet excited states. Using this methodology, we have found that the state populated by the initial excitation is the S2 (ππ*) state, which decays very efficiently to the S1 (nπ*) state at a pedal-like non-rotated geometry. On the S1 state, relaxation leads to a rotated geometry where the system decays to the ground state, in which further relaxation can lead to either the trans or cis geometries. However the S1/S0 CI seam also extends to planar geometries, so this reaction path is also accessible for rotation-constrained systems. Our results explain the experimental observations satisfactorily.

Journal article

Vacher M, Albertani FEA, Jenkins AJ, Polyak I, Bearpark M, Robb MAet al., 2016, Electron and nuclear dynamics following ionisation of modified bismethylene-adamantane, Faraday Discussions, Vol: 194, Pages: 95-115, ISSN: 1364-5498

We have simulated the coupled electron and nuclear dynamics using the Ehrenfest method upon valence ionisation of modified bismethylene-adamantane (BMA) molecules where there is an electron transfer between the two π bonds. We have shown that the nuclear motion significantly affects the electron dynamics after a few fs when the electronic states involved are close in energy. We have also demonstrated how the non-stationary electronic wave packet determines the nuclear motion, more precisely the asymmetric stretching of the two π bonds, illustrating “charge-directed reactivity”. Taking into account the nuclear wave packet width results in the dephasing of electron dynamics with a half-life of 8 fs; this eventually leads to the equal delocalisation of the hole density over the two methylene groups and thus symmetric bond lengths.

Journal article

Jenkins AJ, Vacher M, Bearpark MJ, Robb MAet al., 2016, Nuclear spatial delocalization silences electron density oscillations in 2-phenyl-ethyl-amine (PEA) and 2-phenylethyl-N,N-dimethylamine (PENNA) cations (vol 144, 104110, 2016), JOURNAL OF CHEMICAL PHYSICS, Vol: 144, ISSN: 0021-9606

Journal article

Jenkins AJ, Vacher M, Bearpark MJ, Robb MAet al., 2016, Nuclear spatial delocalization silences electron density oscillations in 2-phenyl-ethyl-amine (PEA) and 2-phenylethyl-N,N-dimethylamine (PENNA) cations, Journal of Chemical Physics, Vol: 144, ISSN: 1089-7690

We simulate electron dynamics following ionization in 2-phenyl-ethyl-amine and 2-phenylethyl-N,N-dimethylamine as examples of systems where 3 coupled cationic states are involved. We study two nuclear effects on electron dynamics: (i) coupled electron-nuclear motion and (ii) nuclear spatial delocalization as a result of the zero-point energy in the neutral molecule. Within the Ehrenfest approximation, our calculations show that the coherent electron dynamics in these molecules is not lost as a result of coupled electron-nuclear motion. In contrast, as a result of nuclear spatial delocalization, dephasing of the oscillations occurs on a time scale of only a few fs, long before any significant nuclear motion can occur. The results have been rationalized using a semi-quantitative model based upon the gradients of the potential energy surfaces.

Journal article

Vigor WA, Spencer JS, Bearpark MJ, Thom AJWet al., 2016, Understanding and improving the efficiency of full configuration interaction quantum Monte Carlo, JOURNAL OF CHEMICAL PHYSICS, Vol: 144, ISSN: 0021-9606

Journal article

McArdle I, Fare C, Bearpark M, Thomas G, Butcher S, Tomlinson C, Mueller M, Burbidge S, Lawlor S, Ferrer J, Rzepa H, Harvey M, Mclean A, Mason Net al., 2015, Research Data Management 'Green Shoots' Pilot Programme, Final Reports, Research Data Management 'Green Shoots' Pilot Programme, Final Reports

This document contains the final reports of six Research Data Management "Green Shoots" projects run at Imperial College in 2014.

Report

Sanchez-Gonzalez A, Barillot TR, Squibb RJ, Kolorenc P, Agaker M, Averbukh V, Bearpark MJ, Bostedt C, Bozek JD, Bruce S, Montero SC, Coffee RN, Cooper B, Cryan JP, Dong M, Eland JHD, Fang L, Fukuzawa H, Guehr M, Ilchen M, Johnsson AS, Liekhus-S C, Marinelli A, Maxwell T, Motomura K, Mucke M, Natan A, Osipov T, Ostlin C, Pernpointner M, Petrovic VS, Robb MA, Sathe C, Simpson ER, Underwood JG, Vacher M, Walke DJ, Wolf TJA, Zhaunerchyk V, Rubensson J-E, Berrah N, Bucksbaum PH, Ueda K, Feifel R, Frasinski LJ, Marangos JPet al., 2015, Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 48, ISSN: 0953-4075

Journal article

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