Quantum Monte Carlo (QMC) methods[1] have been becoming a powerful technique for the study of the electronic structure of molecules and solids, thanks to theoretical developments and to the resources from high performance computing. The combined use of QMC methods and of the Jastrow Antisymmetrized Geminal Power (JAGP) ansatz[2] by means of the TurboRVB package[3] represents an accurate computational protocol applied to several fields of physics and chemistry.
In this seminar our results in various problems of quantum chemistry by the JAGP with variational and diffusion Monte Carlo are reported. First, the performances of the JAGP for diradical molecules is shown, pointing out analogies and differences with traditional quantum chemistry approaches : the prototypical example given by the torsion of the ethylene molecule[4], the retinal minimal model used to study the properties of the full chromophore[5] involved in the mechanism of the vision and the disjoint non-KekuleÌ diradical tetramethyleneethane[6].
Second, a recent development of TurboRVB for the study of the interaction of the molecular target with an external field[7] has allowed us to compute the static polarizability of the ethyne in a finite field scheme[8], and to describe the role of the protein environment in the characterization of the structural and optical properties of the retinal chromophore[7,9].
Finally, the geometry optimization of a †large†chromophore as the peridinin molecule has been performed[10], and the interplay between the gas-phase geometric features and excited states has been analyzed.
References :
[1] Hammond, B. L. ; Lester, W. A., Jr. ; Reynolds, P. J. Monte Carlo Methods in Ab-Initio Quantum Chemistry ; World Scientific, 1994.
[2] Casula, M. ; Sorella, S. J. Chem. Phys. 2003, 119, 6500–6511.
[3] Sorella, S. TurboRVB Quantum Monte Carlo package (accessed date May 21, 2015). http://people.sissa.it/~sorella/web/index.html
[4] Zen, A. ; Coccia, E. ; Luo, Y. ; Sorella, S. ; Guidoni, L. J. Chem. Theory Comput. 2014, 10, 1048–1061.
[5] Zen, A. ; Coccia, E. ; Gozem, S. ; Olivucci, M. ; Guidoni, L. J. Chem. Theory Comput. 2015, 11, 992–1005.
[6] Barborini, M. ; Coccia, E. J. Chem. Theory Comput. submitted.
[7] Coccia, E. ; Varsano, D. ; Guidoni, L. J. Chem. Theory Comput. 2013, 9, 8–12.
[8] Coccia, E. ; Chernomor, O. ; Barborini, M. ; Sorella, S. ; Guidoni, L. J. Chem. Theory Comput. 2012, 8, 1952–1962.
[9] Coccia, E. ; Guidoni, L. J. Comput. Chem. 2012, 33, 2332–2339.
[10] Coccia, E. ; Varsano, D. ; Guidoni, L. J. Chem. Theory Comput. 2014, 10, 501–506.