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Low-Lying Excited States of Ethylene by Quantum Monte Carlo

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In the recent article by Barborini, Sorella and Guidoni published on the Journal of chemical Theory & Computation[1], the structural optimization method developed by S. Sorella[2] has been applied to the study of the structures of the ground state and first excited triplet states of the ethylene molecule. All the calculations were done using an accurate and compact wave function based on Pauling's resonating valence bond representation: the Jastrow Antisymmetrized Geminal Power (JAGP). All structural and wave function parameters are optimized, including coefficients and exponents of the Gaussian primitives of the AGP and the Jastrow atomic orbitals. Bond lengths and bond anglesare calculated with a statistical error of about 0.1% and are in good agreement with the available experimental data. The Variational and Diffusion Monte Carlo calculations estimate vertical and adiabatic excitation energies in the ranges 4.623(10), 4.688(5) eV and 3.001(5)‚ 3.091(5) eV, respectively. The adiabatic gap, which is in line with other correlated quantumchemistry methods, is slightly higher than the value estimated by recent photodissociation experiments. Our results demonstratehow Quantum Monte Carlo calculations have become a promising and computationally affordable tool for the structural optimization of correlated molecular systems.

 

Copertina_Ethylene

Figure 1. We represent the geometrical relaxation of the triplet vertical excitation to it's adiabatic equilibrium, has shown in the movie: Triplet Ethylene geometrical optimization through Quantum Monte Carlo methods

 

[1] Barborini M., Sorella S., Guidoni L., J. Chem. Theory Comput. 8,1260-1269 (2012)

[2] S. Sorella and S. Capriotti, J. Chem. Phys. 133, 234111 (2010)

 

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