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UC.PT

Theoretical & Computational Chemistry

Luís Pedro Viegas

Academic background

Finished undergraduate studies in Chemistry in 2002 and PhD in Theoretical Chemistry under the supervision of Professor António Varandas in 2008, both in University of Coimbra. 

Research contracts:

2022 - Present - Assistant Researcher at the Coimbra Chemistry Center

2020 - 2022 - Junior Researcher at the Coimbra Chemistry Center

2019-2020 - Post-doctoral fellow at the Coimbra Chemistry Center

2016-2018 - Assistant Professor/AIAS-COFUND (Marie Skłodowska-Curie) Fellow in Chemistry at the Aarhus Institute of Advanced Studies (AIAS), Aarhus University, Aarhus, Denmark

2008-2016 - Post-doctoral fellow at the Coimbra Chemistry Center

Areas of interest

  • Predict accurate atmospheric lifetimes for fluorinated oxygenated volatile organic compounds (FOVOCs), which depend on the rate constants associated with their main tropospheric degradation pathway: OH-initiated oxidation reaction. The conformational complexity of FOVOCs can be accounted for with multiconformer transition state theory (MC-TST), for which our recently developed computational protocol (https://doi.org/10.1021/acs.jpca.1c00683) for bimolecular reactions provides a cost-effective way of theoretically calculating rate constants that were, until recently, too complex to tackle. This methodology, along with the calculation of global warming potentials (GWP) can guide the discovery of new green molecules which can potentially substitute powerful greenhouse gases like hydrofluorocarbons, which are being phased-down according to the Kigali Amendment to the Montreal Protocol (October 2016).
  • Predict the rate constants of spin-forbidden reactions with the use of non-adiabatic transition state theory (NA-TST). Specifically, we aim at studying reactions taking place at cryogenic temperatures, for which a thermal over-the-barrier process is ruled out, therefore being solely controlled by quantum mechanical tunneling (QMT, light- or heavy-atom). To account for the QMT, we employ the weak-coupling formulation of NA-TST which, apart from our own recent work (https://doi.org/10.1002/anie.202006640), has never been utilized for calculating vibrational ground-state QMT reactions rates. Such a methodology is expected to provide a deep understanding of a variety of chemical reactions, particularly the ones controlled by the less common heavy-atom QMT.


Publications:

"With a little help from our (AI) friend: A general transition state sampling method for tropospheric hydrogen abstraction reactions" L. P. Viegas and B. R. L. Galvão, Atmos. Environ. 328, 120515 (2024) http://dx.doi.org/10.1016/j.atmosenv.2024.120515

"A Multiconformational Transition State Theory Approach to OH Tropospheric Degradation of Fluorotelomer Aldehydes" L. P. Viegas, ChemPhysChem 24, e202300259 (2023) http://dx.doi.org/10.1002/cphc.202300259

"A computer-based solution to the oxidation kinetics of fluorinated and oxygenated volatile organic compounds" L. P. Viegas and F. Jensen, Environ. Sci.: Atmos. 3, 855 (2023) http://dx.doi.org/10.1039/d2ea00164k

"Multiconformer transition state theory rate constant and branching ratios for the OH-initiated reaction of CH3OCF2CHF2 and its primary product, HC(O)OCF2CHF2" L. P. Viegas, J. Phys. Org. Chem. 36, e4470 (2023) http://dx.doi.org/10.1002/poc.4470

"Atmospheric degradation of two hydrofluoroketones: theoretical rate constants for the gas-phase OH-oxidation of HFK-447mcc and HFK-465mc" L. P. Viegas, Atmosphere 13, 1256 (2022) https://doi.org/10.3390/atmos13081256

"Gas-phase OH-oxidation of 2-butanethiol: Multiconformer transition state theory rate constant with constrained transition state randomization" L. P. Viegas, Chem. Phys. Lett. 803, 139829 (2022) https://doi.org/10.1016/j.cplett.2022.139829

"Theoretical Chemistry of Atmospheric Processes" L. P. Viegas, Atmosphere 13, 309 (2022) https://doi.org/10.3390/atmos13020309 (Editorial)

"Switching on H-tunneling through conformational control" J. P. L. Roque, C. M. Nunes, L. P. Viegas, N. A. M. Pereira, T. M. V. D. Pinho e Melo, P. R. Schreiner and R. Fausto, J. Am. Chem. Soc. 143, 8266 (2021) https://doi.org/10.1021/jacs.1c04329 (Communication)

"Simplified protocol for the calculation of multiconformer transition state theory rate constants applied to tropospheric OH-initiated oxidation reactions" L. P. Viegas, J. Phys. Chem. A 125, 4499 (2021) https://doi.org/10.1021/acs.jpca.1c00683 (Feature Article) 

"Spin-forbidden heavy-atom tunneling in the ring-closure of triplet cyclopentane-1,3-diyl" L. P. Viegas, C. M. Nunes and R. Fausto, Phys. Chem. Chem. Phys. 23, 5797 (2021) https://doi.org/10.1039/D1CP00076D (HOT Article) 

"Glucuronidation of methylated quercetin derivatives: chemical and biochemical approaches" M. L. do Campo-Palacios, A. Alvarez-Hernández, O. Adiji, D. Gamiotea-Turro, A. B. Valerino-Diaz, L. P. Viegas, I. E. Ndukwe, Â. de Fátima, C. Heiss, P. Azidi, G. Pasinetti and R. A. Dixon, J. Agric. Food Chem. 68, 14790 (2020) https://doi.org/10.1021/acs.jafc.0c04500

"Reliability of semiempirical and DFTB methods for the global optimization of the structures of nanoclusters" B. R. L. Galvão, L. P. Viegas, D. R. Salahub and M. P. Lourenço, J. Mol. Model. 26, 303 (2020) http://dx.doi.org/10.1007/s00894-020-04484-4

"Heavy-atom tunneling through crossing potential energy surfaces: cyclization of a triplet 2-formylarylnitrene to a singlet 2,1-benzisoxazole" C. M. Nunes, L. P. Viegas, S. A. Wood, J. P. L. Roque, R. J. McMahon and R. Fausto, Angew. Chem. Int. Ed. 59, 17622 (2020) http://dx.doi.org/10.1002/anie.202006640 (VIP paper)

"Reactivity of α, ω-dihydrofluoropolyethers toward OH predicted by multiconformer transition state theory and the interacting quantum atoms approach" L. P. Viegas and F. Jensen, J. Phys. Chem. A 124, 3460 (2020) http://dx.doi.org/10.1021/acs.jpca.0c02911

"What electronic structure method can be used in the global optimization of nanoclusters?" B. R. L. Galvão and L. P. Viegas, J. Phys. Chem. A 123, 10454 (2019) http://dx.doi.org/10.1021/acs.jpca.9b09309

"Theoretical determination of the OH-initiated oxidation rate constants of α, ω-dialkoxyfluoropolyethers" L. P. Viegas, Theor. Chem. Acc. 138, 65 (2019) http://dx.doi.org/10.1007/s00214-019-2436-z

"Multiconformer transition state theory rate constants for the reaction between OH and α, ω-dimethoxyfluoropolyethers" L. P. Viegas, Int. J. Chem. Kinet. 51, 358 (2019) http://dx.doi.org/10.1002/kin.21259

"Exploring the reactivity of hydrofluoropolyethers toward OH through a cost-effective protocol for calculating multiconformer transition state theory rate constants" L. P. Viegas, J. Phys. Chem. A 122, 9721 (2018) http://dx.doi.org/10.1021/acs.jpca.8b08970

"Assessment of model chemistries for hydrofluoropolyethers: A DFT/M08-HX benchmark study" L. P. Viegas,  Int. J. Quantum Chem. 117, e25381 (2017) https://doi.org/10.1002/qua.25381

"The HO2+(H2O)n+O3 reaction: an overview and recent developments" L. P. Viegas and A. J. C. Varandas, Eur. Phys. J. D 70, 48 (2016) http://dx.doi.org/10.1140/epjd/e2016-60733-5

"Role of (H2O)n (n=2−3) clusters on the HO2+O3 reaction. A theoretical study" L. P. Viegas and A. J. C. Varandas, J. Phys. Chem. B 120, 1560 (2016) http://dx.doi.org/10.1021/acs.jpcb.5b07691

"Mapping the HO3 ground state potential energy surface with DFT: Can we reproduce the MRCI+Q/CBS data?" L. P. Viegas, D. Carolina and A. J. C. Varandas, Chem. Phys. Lett. 620, 61 (2015) http://dx.doi.org/10.1016/j.cplett.2014.12.034

"Coupled-cluster reaction barriers of HO2+H2O+O3: an application of the coupled-cluster//Kohn-Sham density functional theory model chemistry" L. P. Viegas and A. J. C. Varandas, J. Comput. Chem. 35, 507 (2014) http://dx.doi.org/10.1002/jcc.23458

"A detailed test study of barrier heights for the HO2+H2O+O3 reaction with various forms of multireference perturbation theory" L. P. Viegas and A. J. C. Varandas, J. Chem. Phys. 136, 114312 (2012) http://dx.doi.org/10.1063/1.3695371

"Can water be a catalyst on the HO2+H2O+O3 reactive cluster?” L. P. Viegas and A. J. C. Varandas, Chem. Phys. 399, 17 (2011) http://dx.doi.org/10.1016/j.chemphys.2011.04.022

”The HO2+O3 reaction: Current status and prospective work” A. J. C. Varandas and L. P. Viegas, Comput. Theoret. Chem. 965, 291 (2011) http://dx.doi.org/10.1016/j.comptc.2010.09.010

”How well can Kohn-Sham DFT describe the HO2+O3 reaction?” L. P. Viegas, Adriana Branco and A. J. C. Varandas, J. Chem. Theory Comput. 6, 2751 (2010) http://dx.doi.org/10.1021/ct100364x

”The HO2+O3 reaction: ab initio study and implications in atmospheric chemistry” L. P. Viegas and A. J. C. Varandas, J. Chem. Theory Comput. 6, 412 (2010) http://dx.doi.org/10.1021/ct900370q

”Geometric phase effect in the vibrational states of triplet H3+” L. P. Viegas and A. J. C. Varandas, Phys. Rev. A 77, 032505 (2008) http://dx.doi.org/10.1103/PhysRevA.77.032505

“Accurate ab initio based multisheeted double many-body expansion potential energy surface for the three lowest electronic singlet states of H3+” L. P. Viegas, A. Alijah and A. J. C. Varandas, J. Chem. Phys. 126, 074309 (2007) http://dx.doi.org/10.1063/1.2566770

“Symmetry analysis of the vibronic states in the upper conical potential (2 3A') of triplet H3+” L. P. Viegas, A. Alijah and A. J. C. Varandas, J. Phys. Chem. A 109, 3307 (2005) http://dx.doi.org/10.1021/jp0448301

“H3+ in the electronic triplet state” A. J. C. Varandas, A. Alijah, M. Cernei and L. P. Viegas in: Quantum Dynamics at Conical Intersections, CCP6 (Collaborative Computational Project No. 6) Research Monographs, U.K., 31-37 (2004) http://www.ccp6.ac.uk/booklets/CCP6-2004_qdyn_conicint.pdf

 “Accurate double many-body expansion potential energy surface for triplet H3+. II. The upper adiabatic sheet (2 3A')” L. P. Viegas, M. Cernei, A. Alijah and A. J. C. Varandas, J. Chem. Phys. 120, 253 (2004) http://dx.doi.org/10.1063/1.1630023

 “Ro-vibrational states of triplet H3+: The lowest 19 bands” A. Alijah, L. P. Viegas, M. Cernei and A. J. C. Varandas, J. Mol. Spectrosc. 221, 163 (2003) http://dx.doi.org/10.1016/S0022-2852(03)00229-7

“Cone states of tri-hydrogen isotopomers and criterion for the geometric phase effect” A. J. C. Varandas and L. P. Viegas, Chem. Phys. Lett. 367, 625 (2003) http://dx.doi.org/10.1016/S0009-2614(02)01780-3