Open House, ISM in Tachikawa, 2011.7.14統計数理研究所オープンハウス（立川）、H23.7.14ポスター発

Kenta Hongo

本郷 研太

English

RISM (Repository of the Institute of Statistical Mathematics) / 統計数理研究所 学術研究リポジトリ

Quantum Monte Carlo Study of Molecular Crystals Kenta Hongo  Research and Development Center for Data Assimilation, Project Assistant Professor   2011年7月14日 統計数理研究所 オープンハウス  Ab-initio Electronic structure calculations Molecular orbital (MO) methods (HF, CI, CC, etc.) ・Ab-initio methods Density functional theory (DFT) Solid state physics;  a variational problem of minimizing the energy with respect to the electron density ・The Schrodinger equation for many-electron systems  Quantum chemistry; a variational problem of minimizing the energy with respect to the many-electron wavefunction A variety of materials are investigated in experiment: transition metal oxides, and ・Current topics in electronic structure calculations Polymorphism in Molecular Crystals            - the existence of more than one form of a compound Each polymorph has different physical and chemical properties Fluorinated 5,11-bis(triethylsilylethynyl)antradihiophene (diF TES ADT) O. D. Jurchescu, et al, Phys. Rev. B 80, 085201 (2009). e.g. effects of polymorphism on charge transport in organic semiconductors DNTT R. S. Sánchez-Carrera, et al,  J. Phys. Chem. C 114, 2334 (2010). Aspirin P. Veshweshwar, et al, J.Am. Chem. Soc. 127, 16802 (2005) Picene R. Mitsuhashi, et al, Nature 464, 76 (2010). Molecular Crystals Quantum Monte Carlo Methods physical quantity : an expectation value of an operator Monte Carlo sampling according to 3N dimensional distribution  Variational Monte Carlo (VMC); a choice of trial wavefunction Accuracy of results strongly depends on the trial wavefuntion adopted. However, Φ is unknown…. Diffusion Monte Carlo (DMC);  an imaginary time-dependent trial wavefunction that converges to   the exact wavefunction after a long enough interval τ Basic idea of DMC: “Purification” of the trial wavefunction  Iterative operation of the imaginary-time evolution operator  Trial wfn. = (GS) (ES) Trial wfn. (ES) = (GS) Signal(=target) Noise VMC energy Imaginary time steps DMC energy Example taken from NiO calculation. Total Energy (a.u.) para-diiodobenzene (p-DIB) Room-temperature hole mobility = 12 cm2/(V s) Typical π-conjugated organic semiconductors have a room-temperature charge-carrier mobility ≈ 1 cm2/(V s)  L. M. Schwartz and J. F. Horning, Mol. Cryst. 2, 379 (1967). R. S. Sánchez-Carrera, et al. Chem. Mater. 20, 5832 (2008). A semiconductor with high mobility as (opt)electronic devices Polymorphism in p-DIB The α-phase is less stable by ≈0.002 eV/atom than the β-phase at 0 K.   Contrary to experimental results! α-phase (Pbca) β-phase (Pccn) Transition from α- to β-phase occurs at 326 K (The α-phase is more stable than the β-phase at zero temperature) Previous DFT calculations [A. Brillante, et al, J. Cam. Chem. Soc 127, 3038, (2005)]:  Exchange-correlation functional = BLYP functional + Pseudopotential = Troullier-Martins Present Study • DIB is a challenging benchmark system for ab initio methods. • DMC is one of the most promising candidates in light of accuracy and cost. • Purpose of our study        - To investigate the relativities of two DIB polymorphs using DMC and DFT                     (DFT approximations: LDA, PW91, PBE, B3LYP, B3LYP+D)  Results and Discussion Energies at the experimental geometries: relative stability ΔE = E(α) – E(β) (<0: Experiment) -200-150-100-50050100ΔE (meV/unit cell) LDA  PW91 PBE B3LYP DMC -123 29 25 68 -48+/-24 B3LYP+D -155 • The DMC result is consistent with experiment, i.e., a negative ΔE. – The DMC value = - 48 +/- 24 meV – The probability that the DMC value of ΔE has a positive sign is about 4 %. • GGAs and B3LYP predict a positive ΔE. • LDA and B3LYP+D correctly give the sign, but strongly overestimate |ΔE|, compared to DMC. –  It is well-known that LDA frequently overbinds. – The Grimme semiempirical dispersion correction is important.  Summary and Perspective • We studied the relative stabilities of two polymorphs of DIB using DMC and DFT. • The DFT results were inconsistent with experiment. • The DMC results correctly predicts that the α phase is more stable than the β one. • My goal is to exploit molecular crystals for highly-efficient clean energy materials – DMC studies of other molecular crystals are in progress.  Acknowledgement This work was done as a Harvard-Riken collaboration, “HaRIKEN” project. I would like to thank my collaborators, Prof. Alan Aspuru-Guzik, Dr. Mark A. Watson at Harvard University and Dr. Toshiaki Iitaka at RIKEN for their helpful support. 

Quantum Monte Carlo Study of Molecular Crystals

https://ismrepo.ism.ac.jp/?action=repository_action_common_download&item_id=31064&item_no=1&attribute_id=17&file_no=1

Quantum Monte Carlo Study of Molecular Crystals

Abstract

Similar works

Full text

Available Versions

RISM (Repository of the Institute of Statistical Mathematics) / 統計数理研究所学術研究リポジトリ

Quantum Monte Carlo Study of Molecular Crystals

Abstract

Similar works

Full text

Available Versions

RISM (Repository of the Institute of Statistical Mathematics) / 統計数理研究所 学術研究リポジトリ

RISM (Repository of the Institute of Statistical Mathematics) / 統計数理研究所学術研究リポジトリ