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SUMMARY:On-The-Fly AB Initio Semiclassical Dynamics for Computing Vibratio
 nally Resolved Electronic Spectra - Professor Jiří Vaníček (EPFL\, Lau
 sanne)
DTSTART:20171101T141500Z
DTEND:20171101T151500Z
UID:TALK75781@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:To evaluate vibrationally resolved electronic spectra of polya
 tomic molecules\, most modern electronic structure packages still employ t
 he crude global harmonic approximation\, and possibly add an ad hoc anharm
 onicity correction at the end. I will explain how such calculations can be
  improved simply but rigorously by combining Heller’s thawed Gaussian ap
 proximation (TGA) [1] with an on-the-fly ab initio (OTF-AI) scheme. This s
 emiclassical methodology will be explained in general as well as on exampl
 es of absorption\, emission\, photoelectron\, and resonance Raman spectra 
 [2\, 3\, 4\, 5]. On one hand\, the efficiency of the OTF-AI-TGA permits tr
 eating all vibrational degrees of freedom explicitly and on an equal footi
 ng. (Up to 105-dimensional examples will be shown [2].) On the other hand\
 , its improved accuracy succeeds in describing electronic absorption and p
 hotoelectron spectra of ammonia [3]\, chosen as a prototypical example of 
 a floppy molecule exhibiting large amplitude motion\, for which global har
 monic approaches fail. I will explain how the method can be extended [4] i
 n order to go beyond the Franck-Condon approximation and capture the coord
 inate dependence of the transition dipole\; this will be demonstrated on t
 he Herzberg-Teller absorption spectra of the phenyl radical and of benzene
 \, a paradigm of an electronically forbidden\, but vibronically allowed tr
 ansition. Finally\, I will show how a single semiclassical trajectory can 
 be used to quantify the dynamical coupling between vibrational degrees of 
 freedom and help decipher the spectral line shapes\, even without using sy
 mmetry [2].\n \n[1] E. J. Heller\, J. Chem. Phys. 62\, 1544 (1975).\n[2] M
 . Wehrle\, M. Šulc\, and J. Vaníček\, J. Chem. Phys. 140\, 244114 (2014
 ).\n[3] M. Wehrle\, S. Oberli\, and J. Vaníček\, J. Phys. Chem. A 119\, 
 5685 (2015).\n[4] A. Patoz\, T. Begušić\, and J. Vaníček\, in preparat
 ion.\n[5] S. Reynaud\, S. V. Antipov\, and J. Vaníček\, in preparation.\
 n
LOCATION:Department of Chemistry\, Cambridge\, Pfizer lecture theatre
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