Mestrado em Física
URI Permanente para esta coleção
Nível: Mestrado Acadêmico
Ano de início: 1992
Conceito atual na CAPES: 4
Ato normativo: Parecer CES/CNE nº 487/2018, homologado pela Port. MEC 609, publicado no DOU em 18/03/2019.
Periodicidade de seleção: Semestral
Área(s) de concentração: Física
Url do curso: https://fisica.ufes.br/pt-br/pos-graduacao/PPGFis/detalhes-do-curso?id=1508
Navegar
Submissões Recentes
- ItemEstudo da aplicação de métodos de extrapolação ao limite CBS para estados excitados moleculares(Universidade Federal do Espírito Santo, 2025-01-31) Silva, Kessia Claudino da; Mota, Vinícius Cândido; https://orcid.org/0000-0001-8368-0803; http://lattes.cnpq.br/4038237972209273; https://orcid.org/0009-0004-2747-4625; http://lattes.cnpq.br/7602356654660147; Paz, Wendel Silva; https://orcid.org/0000-0001-5737-0633; http://lattes.cnpq.br/8332147920469110; Alves, Márcio Oliveira; https://orcid.org; http://lattes.cnpq.br/2837495576079640In this work high-level ab initio calculations were performed using multiconfigurational methods. The objective of the work is not to propose a new method for energy extrapolation to the complete basis set limit, but to verify if the methods found in the literature and calibrated for ground state systems can also be applied to molecular excited states. A total of 24 systems were considered, and all calculations were performed using the AVXZ basis set (X = D, T, Q, 5 and 6). The analysis of the order of magnitude of the results obtained for the excited states was carried out, and comparisons with the results available in the literature for the ground states were made. Through the use of the USTE protocol, a compatibility was noted between the RMSD obtained for the correlation and MRCI energies extrapolated for the molecular systems in their excited states, in relation to the RMSD found for these systems in their ground states. The HF-E protocol was used to determine the CASSCF energy extrapolated of the first excited state of the molecular systems and, in this case, greater differences in the order of magnitude were found of the RMSD that we calculated, compared to those found in the literature for systems in their ground states. Thus, our work suggests that the USTE method can be applied similarly to excited molecular systems. However, with the results obtained for the CASSCF energy, it was not possible to affirm that the HF-E protocol can be applied to excited molecular systems in a similar way to what was constructed for the ground state. In this case, we raise the possibility of making some adjustments in the computational calculations (which were presented throughout the discussion), and a potential need for protocol calibration for this type of application.
- ItemClassificação espectral de PAHs via deep learning informado pela física(Universidade Federal do Espírito Santo, 2026-03-19) Silva, Geovani Victor Soares da; Souza, Fábio Arthur Leão de; https://orcid.org/0000-0002-6158-7330; http://lattes.cnpq.br/1140962711692698; Pansini, Fernando Nespoli Nassar; https://orcid.org/0000-0001-8984-686X; http://lattes.cnpq.br/7331959117489023; https://orcid.org/0009-0000-2372-0519; http://lattes.cnpq.br/7645514719354805; Mota, Vinícius Cândido; https://orcid.org/0000-0001-8368-0803; http://lattes.cnpq.br/4038237972209273; Marra, Valério; http://orcid.org/0000-0002-7773-1579; http://lattes.cnpq.br/6846011112691877The identification of Polycyclic Aromatic Hydrocarbons (PAHs) in astrophysical environ ments relies on comparing theoretical spectra computed by Density Functional Theory (DFT) with experimental infrared observations. However, the harmonic approximation employed in DFT calculations neglects anharmonic effects, such as non-uniform frequency shifts, Fermi resonances, and combination bands, producing a domain shift that com promises the generalization of deep learning models trained exclusively on theoretical data. This thesis proposes and validates a Spectroscopy-Guided Data Augmentation (SGDA) strategy, based on the stochastic simulation of physical artifacts, to overcome this limitation without requiring costly anharmonic calculations. The methodology rests on three pillars: (i) optimization of the spectral resolution, set at a Full Width at Half Maximum (FWHM) of 6.0 cm−1, which maximizes the geometric separability among chem ical classes; (ii) a physics-informed transformation pipeline, including elastic distortion of the frequency axis, insertion of synthetic peaks, and band masking, algorithmically formalized to ensure reproducibility; and (iii) a One-Dimensional Convolutional Neural Network (1D-CNN) based on the Inception architecture, adapted for multiscale spectral feature extraction. The model was trained on 10,775 theoretical spectra from the NASA Ames PAH IR Spectroscopic Database (PAHdb) and evaluated on 84 matrix-isolation experimental spectra. The Physics-Informed strategy achieved a weighted F1-Score of 0.826 on the experimental test set, significantly outperforming both the harmonic baseline (0.567) and the linear Bjerrum augmentation approach (0.558). Interpretability analyses via Grad-CAM demonstrated that the network bases its decisions on chemically coherent spectral regions: the shoulders of the C–H stretching band (∼ 3050 cm−1) for neutral PAHs, the skeletal deformation modes (1100–1600 cm−1) for PANHs, and signal suppression at high frequencies (> 1700 cm−1) for ionic species. The t-SNE analysis confirmed that the model reduces the distance between the theoretical and experimental domains in latent space, with reductions of up to 36% in centroid distance for the PAH Cation class. The results validate the hypothesis that incorporating physical knowledge into neural network training constitutes an effective domain adaptation strategy for computational spectroscopy, opening perspectives for the automated analysis of observational data from the James Webb Space Telescope (JWST)
- ItemEstudo computacional de folhas de óxido de grafeno com variados graus de oxidação(Universidade Federal do Espírito Santo, 2025-10-14) Sabadini, Igor Broseguini; Co-orientador1; https://orcid.org; https://lattes.cnpq.br; Orientador1; https://orcid.org/; https://lattes.cnpq.br; https://orcid.org/0009-0000-7583-6919; https://lattes.cnpq.br; 1º membro da banca; https://orcid.org; https://lattes.cnpq.br; 2º membro da banca; https://orcid.org; https://lattes.cnpq.br; 3º membro da banca; https://orcid.org; https://lattes.cnpq.brGraphene and graphene oxide (GO) are materials that show important electronic properties for many applications, for example, in electrochemical, optical, and electronic devices. Although graphene is a difficult to synthesize, GO is, on the other hand, a fairly easy one, and it is possible to obtain graphene starting from GO. Graphene flakes with hydroxyl and epoxy functional groups were analyzed using quantum chemical methods (specifically, density functional theory). Also, the connections between the simulated 13C nuclear magnetic resonance (NMR) spectra and the structure of the system were searched. The study showed that the presence of the functional groups: (i) influences the emergence of peaks between 90 and 60 ppm in the NMR spectrum; (ii) shifts sp2 carbon peaks to the left of the NMR spectrum (increasing the average chemical shifts); (iii) and promotes the unification of 3 peaks in the sp2 carbon range that initially existed without the presence of the functional groups. It is shown that the obtained computational results have a good agreement with the NMR spectral changes observed in experiments of thermal reduction of GO
- ItemSimetrias de Noether em cosmologia: os casos Brans-Dicke e Einstein-aether(Universidade Federal do Espírito Santo, 2025-05-06) Calavorty, Estêvão Belz; Gonçalves, Sérgio Vitorino de Borba; https://orcid.org/0000-0002-8570-9750; http://lattes.cnpq.br/4992784379693871; https://orcid.org/0009-0006-1757-2971; http://lattes.cnpq.br/7156468282416273; Alvarenga, Flavio Gimenes; https://orcid.org/0000-0002-7579-9561; http://lattes.cnpq.br/7169430092692431; Martins, Gabriel Luchini; https://orcid.org/0000-0001-6627-3034; http://lattes.cnpq.br/3344738411070832; Belich Junior, Humberto; https://orcid.org/0000-0002-8795-1735; http://lattes.cnpq.br/3879935393431243; Buffon, Luiz Otávio; https://orcid.org/0000-0001-7771-0842; http://lattes.cnpq.br/5054076130464452The purpose of this work is to carry out a review on Noether’s theorem, based on the Lagrangian and Hamiltonian formalisms, exploring symmetries of this system, as well as their respective conserved quantities. Such quantities are obtained by the theorem, in different applications, from simple cases such as that of a free particle and a harmonic oscillator, to studies associated with Brans-Dicke’s cosmology and the Einstein-aether model. So, with a view to a good review and a notion of applicability in the context of gravitation, we sought to develop more complex cases, as well as to analyze possible applications in future projects.
- ItemEstudo da reatividade de defeitos topológicos no SiC 2D(Universidade Federal do Espírito Santo, 2025-06-03) Almeida, Eduardo Ahnert Rodrigues de; Paz, Wendel Silva; https://orcid.org/0000-0001-5737-0633; http://lattes.cnpq.br/8332147920469110; http://lattes.cnpq.br/5468735492074356; Spalenza, Wesley; https://orcid.org/0000-0001-9644-3938; http://lattes.cnpq.br/2687428810786056; Belich Junior, Humberto; https://orcid.org/0000-0002-8795-1735; http://lattes.cnpq.br/3879935393431243; Pansini, Fernando Néspoli Nassar; https://orcid.org/0000-0001-8984-686X; http://lattes.cnpq.br/7331959117489023In this study, we employed first-principles calculations based on Density Functional Theory to investigate the interaction of diatomic molecules (CO, NO and SO) with two-dimensional SiC monolayers containing 5-8-5 linear defects (585-ELD). Our results indicate that pristine 2D SiC exhibits a band gap of approximately 2.5 eV, while the presence of the 585-ELD introduces electronic states associated with pz orbitals near the Fermi level. Upon characterizing the adsorption of the molecules on 2D SiC with the 585-ELD, the Electronic Density of States (DOS) calculations revealed the formation of hybrid orbitals, indicating a chemisorption process. The calculated adsorption energies were-0.45 eV (CO),-1.38 eV (NO), and-2.88 eV (SO), with respective charge transfers of 0.40|e|, 1.37|e| and 1.71|e| to the molecules, thus characterizing strong chemisorption. We conclude that while this high affinity favors sensor sensitivity, it may hinder molecule desorption and consequently compromise its reusability. For future perspectives, we propose investigating the effects of mechanical strain on the material, using other external stimuli, and extending the study to other molecular species.