More Like this

1. Coupled cluster theory in the condensed phase within the singles‐T density scheme for the environment response

   https://doi.org/10.1002/wcms.1463  

   Caricato, Marco ( January 2020 , WIREs Computational Molecular Science)

   Reliable simulations of molecules in condensed phase require the combination of an accurate quantum mechanical method for the core region, and a realistic model to describe the interaction with the environment. Additionally, this combination should not significantly increase the computational cost of the calculation compared to the corresponding in vacuo case. In this review, we describe the combination of methods based on coupled cluster (CC) theory with polarizable classical models for the environment. We use the polarizable continuum model (PCM) of solvation to discuss the equations, but we also show how the same theoretical framework can be extended to polarizable force fields. The theory is developed within the perturbation theory energy and singles‐T density (PTES) scheme, where the environmental response is computed with the CC single excitation amplitudes as an approximation for the full one‐particle reduced density. The CC‐PTES combination provides the best compromise between accuracy and computational effort for CC calculations in condensed phase, because it includes the response of the environment to the correlation density at the same computational cost of in vacuo CC. We discuss a number of numerical applications for ground and excited state properties, based on the implementation of CC‐PTES with single and double excitations (CCSD‐PTES), which show the reliability and computational efficiency of the method in reproducing experimental or full‐CC data.

   This article is characterized under:

   Electronic Structure Theory > Ab Initio Electronic Structure Methods

   Electronic Structure Theory > Combined QM/MM Methods

   Software > Quantum Chemistry

    

   more » « less
2. Exploiting graphical processing units to enable quantum chemistry calculation of large solvated molecules with conductor‐like polarizable continuum models

   https://doi.org/10.1002/qua.25760  

   Liu, Fang ; Sanchez, David M. ; Kulik, Heather J. ; Martínez, Todd J. ( October 2018 , International Journal of Quantum Chemistry)

   The conductor‐like polarizable continuum model (C‐PCM) with switching/Gaussian smooth discretization is a widely used implicit solvation model in quantum chemistry. We have previously implemented C‐PCM solvation for Hartree‐Fock (HF) and density functional theory (DFT) on graphical processing units (GPUs), enabling the quantum mechanical treatment of large solvated biomolecules. Here, we first propose a GPU‐based algorithm for the PCM conjugate gradient linear solver that greatly improves the performance for very large molecules. The overhead for PCM‐related evaluations now consumes less than 15% of the total runtime for DFT calculations on large molecules. Second, we demonstrate that our algorithms tailored for ground state C‐PCM are transferable to excited state properties. Using a single GPU, our method evaluates the analytic gradient of the linear response PCM time‐dependent density functional theory energy up to 80× faster than a conventional central processing unit (CPU)‐based implementation. In addition, our C‐PCM algorithms are transferable to other methods that require electrostatic potential (ESP) evaluations. For example, we achieve speed‐ups of up to 130× for restricted ESP‐based atomic charge evaluations, when compared to CPU‐based codes. We also summarize and compare the different PCM cavity discretization schemes used in some popular quantum chemistry packages as a reference for both users and developers.

    

   more » « less
3. Evaluation of molecular photophysical and photochemical properties using linear response time-dependent density functional theory with classical embedding: Successes and challenges

   https://doi.org/10.1063/5.0088271  

   Liang, WanZhen ; Pei, Zheng ; Mao, Yuezhi ; Shao, Yihan ( June 2022 , The Journal of Chemical Physics)

   Time-dependent density functional theory (TDDFT) based approaches have been developed in recent years to model the excited-state properties and transition processes of the molecules in the gas-phase and in a condensed medium, such as in a solution and protein microenvironment or near semiconductor and metal surfaces. In the latter case, usually, classical embedding models have been adopted to account for the molecular environmental effects, leading to the multi-scale approaches of TDDFT/polarizable continuum model (PCM) and TDDFT/molecular mechanics (MM), where a molecular system of interest is designated as the quantum mechanical region and treated with TDDFT, while the environment is usually described using either a PCM or (non-polarizable or polarizable) MM force fields. In this Perspective, we briefly review these TDDFT-related multi-scale models with a specific emphasis on the implementation of analytical energy derivatives, such as the energy gradient and Hessian, the nonadiabatic coupling, the spin–orbit coupling, and the transition dipole moment as well as their nuclear derivatives for various radiative and radiativeless transition processes among electronic states. Three variations of the TDDFT method, the Tamm–Dancoff approximation to TDDFT, spin–flip DFT, and spin-adiabatic TDDFT, are discussed. Moreover, using a model system (pyridine–Ag 20 complex), we emphasize that caution is needed to properly account for system–environment interactions within the TDDFT/MM models. Specifically, one should appropriately damp the electrostatic embedding potential from MM atoms and carefully tune the van der Waals interaction potential between the system and the environment. We also highlight the lack of proper treatment of charge transfer between the quantum mechanics and MM regions as well as the need for accelerated TDDFT modelings and interpretability, which calls for new method developments. 

   more » « less
4. State-specific solvation for restricted active space spin–flip (RAS-SF) wave functions based on the polarizable continuum formalism

   https://doi.org/10.1063/5.0091636  

   Alam, Bushra ; Jiang, Hanjie ; Zimmerman, Paul M. ; Herbert, John M. ( May 2022 , The Journal of Chemical Physics)

   The restricted active space spin–flip (RAS-SF) formalism is a particular form of single-reference configuration interaction that can describe some forms of strong correlation at a relatively low cost and which has recently been formulated for the description of charge-transfer excited states. Here, we introduce both equilibrium and nonequilibrium versions of a state-specific solvation correction for vertical transition energies computed using RAS-SF wave functions, based on the framework of a polarizable continuum model (PCM). Ground-state polarization is described using the solvent’s static dielectric constant and in the nonequilibrium solvation approach that polarization is modified upon vertical excitation using the solvent’s optical dielectric constant. Benchmark calculations are reported for well-studied models of photo-induced charge transfer, including naphthalene dimer, C 2 H 4 ⋯C 2 F 4 , pentacene dimer, and perylene diimide (PDI) dimer, several of which are important in organic photovoltaic applications. For the PDI dimer, we demonstrate that the charge-transfer character of the excited states is enhanced in the presence of a low-dielectric medium (static dielectric constant ɛ 0 = 3) as compared to a gas-phase calculation ( ɛ 0 = 1). This stabilizes mechanistic traps for singlet fission and helps to explain experimental singlet fission rates. We also examine the effects of nonequilibrium solvation on charge-separated states in an intramolecular singlet fission chromophore, where we demonstrate that the energetic ordering of the states changes as a function of solvent polarity. The RAS-SF + PCM methodology that is reported here provides a framework to study charge-separated states in solution and in photovoltaic materials. 

   more » « less
5. Prediction of p K a s of Late Transition‐Metal Hydrides via a QM/QM Approach

   https://doi.org/10.1002/jcc.26057  

   Patel, Prajay ; Wang, Jiaqi ; Wilson, Angela K. ( September 2019 , Journal of Computational Chemistry)

   Three implicit solvation models, the conductor‐like polarizable continuum model (C‐PCM), the conductor‐like screening model (COSMO), and universal implicit solvent model (SMD), combined with a hybrid two layer QM/QM approach (ONIOM), were utilized to calculate the pK_avalues, using a direct thermodynamic scheme, of a set of Group 10 transition metal (TM) hydrides in acetonitrile. To obtain the optimal combination of quantum methods for ONIOM calculations with implicit solvation models, the influence of factors, such as the choice of density functional and basis set, the atomic radii used to build a cavity in the solvent, and the size of the model system in an ONIOM scheme, was examined. Additionally, the impact of Grimme's empirical dispersion correction and exact exchange was also investigated. The results were calibrated by experimental data. This investigation provides insight about effective models for the prediction of thermodynamic properties of TM‐containing complexes with bulky ligands. © 2019 Wiley Periodicals, Inc.

    

   more » « less