## Simulating Electron Dynamics of Complex Molecules with Time-Dependent Complete Active Space Configuration Interaction

## Abstract

In this paper, time-dependent electronic structure methods are growing in popularity as tools for modeling ultrafast and/or nonlinear processes, for computing spectra, and as the electronic structure component of mean-field molecular dynamics simulations. Time-dependent configuration interaction (TD-CI) offers several advantages over the widely used real-time time-dependent density functional theory: namely, that it correctly models Rabi oscillations; it offers a spin-pure description of open-shell systems; and a hierarchy of TD-CI methods can be defined that systematically approach the exact solution of the time-dependent Schrodinger equation (TDSE). In this work, we present a novel TD-CI approach that extends TD-CI to large complete active-space configuration expansions. Such extension is enabled by use of a direct configuration interaction approach that eliminates the need to explicitly build, store, or diagonalize the Hamiltonian matrix. Graphics processing unit (GPU) acceleration enables fast solution of the TDSE even for large active spaces—up to 12 electrons in 12 orbitals (853776 determinants) in this work. A symplectic split operator propagator yields long-time norm conservation. We demonstrate the applicability of our approach by computing the response of a large molecule with a strongly correlated ground state, decacene (C _{42}H _{24}), to various pulses (δ-function, transform limited, chirped). Our simulations predict thatmore »

- Authors:

- Michigan State Univ., East Lansing, MI (United States)
- Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)

- Publication Date:

- Research Org.:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)

- Sponsoring Org.:
- USDOE

- OSTI Identifier:
- 1476145

- Grant/Contract Number:
- AC02-76SF00515; FA9550-17-1-0411

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Journal of Chemical Theory and Computation

- Additional Journal Information:
- Journal Volume: 14; Journal Issue: 8; Journal ID: ISSN 1549-9618

- Publisher:
- American Chemical Society

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

### Citation Formats

```
Peng, Wei -Tao, Fales, B. Scott, and Levine, Benjamin G. Simulating Electron Dynamics of Complex Molecules with Time-Dependent Complete Active Space Configuration Interaction. United States: N. p., 2018.
Web. doi:10.1021/acs.jctc.8b00381.
```

```
Peng, Wei -Tao, Fales, B. Scott, & Levine, Benjamin G. Simulating Electron Dynamics of Complex Molecules with Time-Dependent Complete Active Space Configuration Interaction. United States. doi:10.1021/acs.jctc.8b00381.
```

```
Peng, Wei -Tao, Fales, B. Scott, and Levine, Benjamin G. Mon .
"Simulating Electron Dynamics of Complex Molecules with Time-Dependent Complete Active Space Configuration Interaction". United States. doi:10.1021/acs.jctc.8b00381. https://www.osti.gov/servlets/purl/1476145.
```

```
@article{osti_1476145,
```

title = {Simulating Electron Dynamics of Complex Molecules with Time-Dependent Complete Active Space Configuration Interaction},

author = {Peng, Wei -Tao and Fales, B. Scott and Levine, Benjamin G.},

abstractNote = {In this paper, time-dependent electronic structure methods are growing in popularity as tools for modeling ultrafast and/or nonlinear processes, for computing spectra, and as the electronic structure component of mean-field molecular dynamics simulations. Time-dependent configuration interaction (TD-CI) offers several advantages over the widely used real-time time-dependent density functional theory: namely, that it correctly models Rabi oscillations; it offers a spin-pure description of open-shell systems; and a hierarchy of TD-CI methods can be defined that systematically approach the exact solution of the time-dependent Schrodinger equation (TDSE). In this work, we present a novel TD-CI approach that extends TD-CI to large complete active-space configuration expansions. Such extension is enabled by use of a direct configuration interaction approach that eliminates the need to explicitly build, store, or diagonalize the Hamiltonian matrix. Graphics processing unit (GPU) acceleration enables fast solution of the TDSE even for large active spaces—up to 12 electrons in 12 orbitals (853776 determinants) in this work. A symplectic split operator propagator yields long-time norm conservation. We demonstrate the applicability of our approach by computing the response of a large molecule with a strongly correlated ground state, decacene (C42H24), to various pulses (δ-function, transform limited, chirped). Our simulations predict that chirped pulses can be used to induce dipole-forbidden transitions. Simulations of decacene using the 6-31G(d) basis set and a 12 electrons/12 orbitals active space took 20.1 h to propagate for 100 fs with a 1 attosecond time step on a single NVIDIA K40 GPU. Convergence with respect to time step is found to depend on the property being computed and the chosen active space.},

doi = {10.1021/acs.jctc.8b00381},

journal = {Journal of Chemical Theory and Computation},

number = 8,

volume = 14,

place = {United States},

year = {2018},

month = {7}

}

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