Search results for "ab initio"
showing 10 items of 990 documents
Anharmonic Vibrational Spectrum and Experimental Matrix Isolation Study of Thioformic Acid Conformers -- Potential Candidates for Molecular Cloud and…
2021
Thioformic acid (TFA) is the sulfur analog of formic acid, the simplest organic acid. It has three analogues HCOSH, HCSOH, and HCSSH, each of them having two rotational isomeric (rotameric) forms: trans and cis where the trans form is energetically more stable. In this article, we study computational energetics and anharmonic vibrational spectrum of TFA including overtone and combination vibrations. We also studied experimental photoisomerization and photodecomposition channels of HCOSH molecules with different wavelengths. We suggest that TFA is a potential sulfur containing candidate molecule for interstellar and planetary observations and discuss these in a light of different radiation e…
Valence-band splitting energies in wurtzite InP nanowires : Photoluminescence spectroscopy and ab initio calculations
2010
We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on “ab initio” calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, r…
Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization
2000
In this paper we use ab initio multiconfigurational second-order perturbation theory to establish the intrinsic photoisomerization path model of retinal chromophores. This is accomplished by computing the ground state ( S 0 ) and the first two singlet excited-state ( S 1 , S 2 ) energies along the rigorously determined photoisomerization coordinate of the rhodopsin chromophore model 4- cis -γ-methylnona-2,4,6,8-tetraeniminium cation and the bacteriorhodopsin chromophore model all- trans -hepta-2,4,6-trieniminium cation in isolated conditions. The computed S 2 and S 1 energy profiles do not show any avoided crossing feature along the S 1 reaction path and maintain an energy gap >20 kcal⋅…
Ultrafast Electron Transfer in Photosynthesis: Reduced Pheophytin and Quinone Interaction Mediated by Conical Intersections
2007
The mechanism of electron transfer (ET) from reduced pheophytin (Pheo−) to the primary stable photosynthetic acceptor, a quinone (Q) molecule, is addressed by using high‐level ab initio computations and realistic molecular models. The results reveal that the ET process involving the (Pheo−+Q) and (Pheo+Q−) oxidation states can be essentially seen as an ultrafast radiationless transition between the two hypersurfaces taking place via conical intersections (CIs) and it is favoured when the topology of the interacting moieties make possible some overlap between the lowest occupied molecular orbitals (LUMO) of the two systems. Thus, it is anticipated that large scale motions, which are difficul…
Ab initioquality neural-network potential for sodium
2010
An interatomic potential for high-pressure high-temperature (HPHT) crystalline and liquid phases of sodium is created using a neural-network (NN) representation of the ab initio potential energy surface. It is demonstrated that the NN potential provides an ab initio quality description of multiple properties of liquid sodium and bcc, fcc, cI16 crystal phases in the P-T region up to 120 GPa and 1200 K. The unique combination of computational efficiency of the NN potential and its ability to reproduce quantitatively experimental properties of sodium in the wide P-T range enables molecular dynamics simulations of physicochemical processes in HPHT sodium of unprecedented quality.
Ab Initio Computations of O and AO as well as ReO2, WO2 and BO2-Terminated ReO3, WO3, BaTiO3, SrTiO3 and BaZrO3 (001) Surfaces
2022
This research received funding from the Latvian-Ukraine cooperation Project No. LV/UA-2021/5. The Institute of Solid State Physics, University of Latvia (Latvia), as the Centre of Excellence, has received funding from the European Unions Horizon 2020 Framework Programme H2020-WIDESPREAD01-2016-2017-Teaming Phase2 under Grant Agreement No. 739508, project CAMART2.
Energy and radiative properties of the (3)Π1 and (5)Σ+1 states of RbCs: Experiment and theory
2017
We combined high-resolution Fourier-transform spectroscopy and large-scale electronic structure calculation to study energy and radiative properties of the high-lying $(3)^{1}\mathrm{\ensuremath{\Pi}}$ and $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ states of the RbCs molecule. The laser-induced $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+},(4)^{1}\mathrm{\ensuremath{\Sigma}}^{+},(3)^{1}\mathrm{\ensuremath{\Pi}}\ensuremath{\rightarrow}A(2)^{1}\mathrm{\ensuremath{\Sigma}}^{+}\ensuremath{\sim} b(1)^{3}\mathrm{\ensuremath{\Pi}}$ fluorescence (LIF) spectra were recorded by the Bruker IFS-125(HR) spectrometer in the frequency range $\ensuremath{\nu}\ensuremath{\in}[5500,10\phantom{\rule{0.16em}{0ex}}00…
Electronic structure of Rf+ (Z=104) from ab initio calculations
2021
We report calculation of the energy spectrum and the spectroscopic properties of the superheavy element ion: ${\mathrm{Rf}}^{+}$. We use the four-component relativistic Dirac-Coulomb Hamiltonian and the multireference configuration interaction model to tackle the complex electronic structure problem that combines strong relativistic effects and electron correlation. We determine the energies of the ground and the low-lying excited states of ${\mathrm{Rf}}^{+}$, which originate from the $7{s}^{2}6{d}^{1},\phantom{\rule{0.28em}{0ex}}7{s}^{1}6{d}^{2},\phantom{\rule{0.28em}{0ex}}7{s}^{2}7{p}^{1}$, and $7{s}^{1}6{d}^{1}7{p}^{1}$ configurations. The results are discussed vis-\`a-vis the lighter h…
Systematic analysis of the peripherality of the Be10(d,p)Be11 transfer reaction and extraction of the asymptotic normalization coefficient of Be11 bo…
2018
We reanalyze the experiment of Schmitt et al. on the $^{10}\mathrm{Be}(d,p)^{11}\mathrm{Be}$ transfer reaction [Phys. Rev. Lett. 108, 192701 (2012)] by exploring the beam-energy and angular ranges at which the reaction is strictly peripheral. We consider the adiabatic distorted wave approximation (ADWA) to model the reaction and use a Halo-EFT description of $^{11}\mathrm{Be}$ to systematically explore the sensitivity of our calculations to the short-range physics of the $^{10}\mathrm{Be}\ensuremath{-}n$ wave function. We find that by selecting the data at low beam energy and forward scattering angle the calculated cross sections scale nearly perfectly with the asymptotic normalization coef…
Isospin symmetry in B(E2) values: Coulomb excitation study of Mg21
2019
The Tz=−32 nucleus 21Mg has been studied by Coulomb excitation on 196Pt and 110Pd targets. A 205.6(1)-keV γ-ray transition resulting from the Coulomb excitation of the 52+ ground state to the first excited 12+ state in 21Mg was observed for the first time. Coulomb excitation cross-section measurements with both targets and a measurement of the half-life of the 12+ state yield an adopted value of B(E2;52+→12+)=13.3(4) W.u. A new excited state at 1672(1) keV with tentative 92+ assignment was also identified in 21Mg. This work demonstrates a large difference in the B(E2;52+→12+) value between T=32, A=21 mirror nuclei. The difference is investigated in the shell-model framework employing both i…