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SUMMARY:Selected CI and Jastrow-free QMC methods for Chemistry - Dr Pierre
 -Francois Loos\, Université de Toulouse
DTSTART:20180516T131500Z
DTEND:20180516T141500Z
UID:TALK97207@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:In this talk\, I will present some of our recent advances on s
 elected configuration interaction (sCI) and quantum Monte Carlo (QMC) meth
 ods.\nIn particular\, I will detail our protocol to deterministically cons
 truct nodal surfaces within QMC using the sCI algorithm CIPSI (Configurati
 on Interaction using a Perturbative Selection made Iteratively) [1]. In co
 ntrast to standard QMC implementations\, these nodes can be systematically
  and deterministically improved by increasing the size of the sCI expansio
 n. The present methodology will be illustrated on the transition metal sul
 fide molecule FeS [2]\, which is particularly challenging due to the proxi
 mity of two low-energy electronic states of different spatial symmetry (se
 e Fig. 1).\nResults on the excited states of small organic molecules will 
 also be presented\, and we are going to show that\, by using small multide
 terminant expansions without Jastrow factor\, one can obtain highly accura
 te vertical transition energies.\nI will also present a new way of introdu
 cing the explicit correlation between electrons within the configu- ration
  interaction (CI) method via a dressing of the CI matrix [3]. Compared to 
 other explicitly-correlated methods\, this dressing strategy has the advan
 tage of introducing the explicit correlation at a relatively low computati
 onal cost [4]. The present idea is completely general and can be applied t
 o any type of trun- cated\, full\, or even selected CI method.\n          
                                                                           
                                                                           
                  Figure 1: Deterministic construction of nodal surfaces wi
 thin QMC for FeS\n[1] B. Huron\, J. P. Malrieu\, and P. Rancurel\, J. Chem
 . Phys. 58\, 5745 (1973).\n[2] A.Scemama\,Y.Garniron\,M.CaffarelandP.F.Loo
 s\,J.Chem.TheoryComput.14\,1395(2018). [3] J.-L. Heuilly and J.-P. Malrieu
 \, Chem. Phys. Lett. 199\, 545 (1992).\n[4] G. M. J. Barca and P. F. Loos\
 , J. Chem. Phys. 147\, 024103 (2017).
LOCATION:Department of Chemistry\, Cambridge\, Unilever lecture theatre
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