scholarly journals Representation of the QM Subsystem for Long-Range Electrostatic Interaction in Non-Periodic Ab Initio QM/MM Calculations

Molecules ◽  
2018 ◽  
Vol 23 (10) ◽  
pp. 2500 ◽  
Author(s):  
Xiaoliang Pan ◽  
Edina Rosta ◽  
Yihan Shao
Keyword(s):  
Electron Density ◽  
Long Range ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Switching Function ◽  
Excitation Energies ◽  
Functional Theory ◽  
Vertical Excitation ◽  
Distance Cutoff ◽  
Switching Functions

In QM/MM calculations, it is essential to handle electrostatic interactions between the QM and MM subsystems accurately and efficiently. To achieve maximal efficiency, it is convenient to adopt a hybrid scheme, where the QM electron density is used explicitly in the evaluation of short-range QM/MM electrostatic interactions, while a multipolar representation for the QM electron density is employed to account for the long-range QM/MM electrostatic interactions. In order to avoid energy discontinuity at the cutoffs, which separate the short- and long-range QM/MM electrostatic interactions, a switching function should be utilized to ensure a smooth potential energy surface. In this study, we benchmarked the accuracy of such hybrid embedding schemes for QM/MM electrostatic interactions using different multipolar representations, switching functions and cutoff distances. For test systems (neutral and anionic oxyluciferin in MM (aqueous and enzyme) environments), the best accuracy was acquired with a combination of QM electrostatic potential (ESP) charges and dipoles and two switching functions (long-range electrostatic corrections (LREC) and Switch) in the treatment of long-range QM/MM electrostatics. It allowed us to apply a 10Å distance cutoff and still obtain QM/MM electrostatics/polarization energies within 0.1 kcal/mol and time-dependent density functional theory (TDDFT)/MM vertical excitation energies within 10−3 eV from theoretical reference values.

How big is big? Separation by conventional methods, X-ray and electronic structures of positional isomers of bis-tert-butylisocyano adduct of 2(3),9(10),16(17),23(24)-tetrachloro-3(2),10(9),17(16),24(23)-tetra(2,6-di-iso-propylphenoxy)-phthalocyaninato iron(II) complex

2016 ◽  
Vol 20 (01n04) ◽  
pp. 337-351 ◽  
Author(s):  
Derrick R. Anderson ◽  
Pavlo V. Solntsev ◽  
Hannah M. Rhoda ◽  
Victor N. Nemykin
Keyword(s):  
Electronic Structures ◽  
Density Functional ◽  
Positional Isomers ◽  
Excitation Energies ◽  
Functional Theory ◽  
X Ray ◽  
Vertical Excitation ◽  
X Ray Crystallography ◽  
Tddft Calculations ◽  
Insight Into

A presence of bulky 2,6-di-iso-propylphenoxy groups in bis-tert-butylisocyano adduct of 2(3),9(10),16(17),23(24)-tetrachloro-3(2),10(9),17(16),24(23)-tetra(2,6-di-iso-propylphenoxy)-phthalocyaninato iron(II) complex allows separation of two individual positional isomers and a mixture of the remaining two isomers using conventional chromatography. X-ray structures of “[Formula: see text]” and “[Formula: see text]” isomers were confimed by X-ray crystallography. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations of each individual positional isomer allowed insight into their electronic structures and vertical excitation energies, which were correlated with the experimental UV-vis and MCD spectra.

scholarly journals Cross-conjugation controls the stabilities and photophysical properties of heteroazoarene photoswitches

2021 ◽  
Author(s):  
Daniel Adrion ◽  
Steven Lopez
Keyword(s):  
High Throughput Screening ◽  
Density Functional ◽  
Photophysical Properties ◽  
Photochemical Reactions ◽  
Free Energies ◽  
Excitation Energies ◽  
Functional Theory ◽  
Vertical Excitation ◽  
Screening Study

Azoarene photoswitches are versatile molecules that interconvert from their E-isomer to their Z-isomer with light. Azobenzene is a prototypical photoswitch but its derivatives can be poorly suited for in vivo applications such as photopharmacology due to undesired photochemical reactions promoted by ultraviolet light and its relatively short half-life (t1/2) of the Z-isomer (2 days). Experimental and computational studies suggest that these properties (λmax of the E isomer and t1/2 of the Z-isomer) are inversely related. We identified isomeric azobisthiophenes and azobisfurans from a high-throughput screening study of 1700 azoarenes as photoswitch candidates with improved λmax and t1/2 values relative to azobenzene. We used density functional theory to predict the activation free energies, reaction free energies, and vertical excitation energies of the E- and Z-isomers of 2,2- and 3,3-substituted azobisthiophenes and azobisfurans. The half-lives depend on whether the heterocycles are 𝜋-conjugated or cross-conjugated with the diazo 𝜋-bond. The 2,2-substituted azoarenes both have t1/2 values on the scale of 1 hour, while the 3,3-analogues have computed half-lives of 40 (thiophene) and 230 (furan) years. The 2,2-substituted heteroazoarenes have significantly higher λmax absorptions than their 3,3-substituted analogs: 76 nm for azofuran and 77 nm for azothiophene.

Excitation energies expressed as orbital energies of Kohn–Sham density functional theory with long‐range corrected functionals

2020 ◽  
Vol 41 (14) ◽  
pp. 1368-1383 ◽  
Author(s):  
Kimihiko Hirao ◽  
Bun Chan ◽  
Jong‐Won Song ◽  
Kamala Bhattarai ◽  
Subrata Tewary
Keyword(s):  
Density Functional Theory ◽  
Long Range ◽  
Density Functional ◽  
Excitation Energies ◽  
Functional Theory ◽  
Orbital Energies

scholarly journals A statistical thermodynamics view of electron density polarisation: application to chemical selectivity

2020 ◽  
Vol 22 (41) ◽  
pp. 23553-23562
Author(s):  
Frédéric Guégan ◽  
Vincent Tognetti ◽  
Jorge I. Martínez-Araya ◽  
Henry Chermette ◽  
Lynda Merzoud ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Heat Exchange ◽  
Electron Density ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Statistical Thermodynamics ◽  
Conceptual Density Functional Theory ◽  
Functional Theory ◽  
Effective Work ◽  
Chemical Selectivity

A fundamental link between conceptual density functional theory and statistical thermodynamics is herein drawn, showing that intermolecular electrostatic interactions can be understood in terms of effective work and heat exchange.

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