scholarly journals Calculating free energies of organic molecules on insulating substrates

2017 ◽  
Vol 8 ◽  
pp. 667-674
Author(s):  
Julian Gaberle ◽  
David Z Gao ◽  
Alexander L Shluger
Keyword(s):  
Free Energy ◽  
Organic Molecules ◽  
Computational Cost ◽  
Potential Of Mean Force ◽  
Free Energies ◽  
Energy Profiles ◽  
Integration Techniques ◽  
Ring Structures ◽  
Anchoring Groups ◽  
Insulating Substrates

The challenges and limitations in calculating free energies and entropies of adsorption and interaction of organic molecules on an insulating substrate are discussed. The adhesion of 1,3,5-tri(4'-cyano-[1,1'-biphenyl]-4-yl)benzene (TCB) and 1,4-bis(4-cyanophenyl)-2,5-bis(decyloxy)benzene (CDB) molecules to step edges on the KCl(001) surface and the formation of molecular dimers were studied using classical molecular dynamics. Both molecules contain the same anchoring groups and benzene ring structures, yet differ in their flexibility. Therefore, the entropic contributions to their free energy differ, which affects surface processes. Using potential of mean force and thermodynamic integration techniques, free energy profiles and entropy changes were calculated for step adhesion and dimer formation of these molecules. However, converging these calculations is nontrivial and comes at large computational cost. We illustrate the difficulties as well as the possibilities of applying these methods towards understanding dynamic processes of organic molecules on insulating substrates.

scholarly journals A Computational Protocol Combining DFT and Cheminformatics for Prediction of pH-Dependent Redox Potentials

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 3978
Author(s):  
Rocco Peter Fornari ◽  
Piotr de Silva
Keyword(s):  
Organic Molecules ◽  
Ph Value ◽  
Computational Cost ◽  
Legendre Transform ◽  
Good Prediction ◽  
Redox Potentials ◽  
Free Energies ◽  
Hybrid Functional ◽  
Data Set ◽  
State Changes

Discovering new materials for energy storage requires reliable and efficient protocols for predicting key properties of unknown compounds. In the context of the search for new organic electrolytes for redox flow batteries, we present and validate a robust procedure to calculate the redox potentials of organic molecules at any pH value, using widely available quantum chemistry and cheminformatics methods. Using a consistent experimental data set for validation, we explore and compare a few different methods for calculating reaction free energies, the treatment of solvation, and the effect of pH on redox potentials. We find that the B3LYP hybrid functional with the COSMO solvation method, in conjunction with thermal contributions evaluated from BLYP gas-phase harmonic frequencies, yields a good prediction of pH = 0 redox potentials at a moderate computational cost. To predict how the potentials are affected by pH, we propose an improved version of the Alberty-Legendre transform that allows the construction of a more realistic Pourbaix diagram by taking into account how the protonation state changes with pH.

MOLECULAR SIMULATION OF α-TOCOPHEROL PASSING ACROSS DPPC LIPID USING POTENTIAL OF MEAN FORCE AND ACCELERATED MOLECULAR DYNAMICS METHOD

2013 ◽  
Vol 12 (08) ◽  
pp. 1341011 ◽  
Author(s):  
FANCUI MENG
Keyword(s):  
Molecular Dynamics ◽  
Free Energy ◽  
Binding Free Energy ◽  
Computation Time ◽  
Potential Of Mean Force ◽  
Accelerated Molecular Dynamics ◽  
Energy Profiles ◽  
Lipid System ◽  
Dynamics Method ◽  
Free Energy Profiles

In this paper the process of α-tocopherol (TCP) passing across DPPC membrane was simulated using both the potential of mean force (PMF) and the accelerated molecular dynamics (aMD) methods, respectively. Energy properties, hydrogen bonds and orientation have been compared between these two methods and several conclusions have been obtained. The results indicate that TCP tends to stay at z = 1.2 nm of lipid bilayer. The binding free energy profiles of these two methods are alike. All these show that aMD could obtain comparable results as PMF method, while needs less computation time and resources. Therefore, aMD method could be used as an alternative method for prediction of transport properties of drug-lipid system.

scholarly journals Approaches for calculating solvation free energies and enthalpies demonstrated with an update of the FreeSolv database

2017 ◽  
Author(s):  
Guilherme Duarte Ramos Matos ◽  
Daisy Y. Kyu ◽  
Hannes H. Loeffler ◽  
John D. Chodera ◽  
Michael R. Shirts ◽  
...  
Keyword(s):  
Free Energy ◽  
Organic Molecules ◽  
Molecular Simulations ◽  
General Purpose ◽  
Free Energies ◽  
Energy Functions ◽  
Neutral Compounds ◽  
Aqueous Solvation ◽  
Solvation Free Energies

AbstractSolvation free energies can now be calculated precisely from molecular simulations, providing a valuable test of the energy functions underlying these simulations. Here, we briefly review “alchemical” approaches for calculating the solvation free energies of small, neutral organic molecules from molecular simulations, and illustrate by applying them to calculate aqueous solvation free energies (hydration free energies). These approaches use a non-physical pathway to compute free energy differences from a simulation or set of simulations and appear to be a particularly robust and general-purpose approach for this task. We also present an update (version 0.5) to our FreeSolv database of experimental and calculated hydration free energies of neutral compounds and provide input files in formats for several simulation packages. This revision to FreeSolv provides calculated values generated with a single protocol and software version, rather than the heterogeneous protocols used in the prior version of the database. We also further update the database to provide calculated enthalpies and entropies of hydration and some experimental enthalpies and entropies, as well as electrostatic and nonpolar components of solvation free energies.

MOLECULAR DYNAMICS SIMULATIONS OF DNA DIMERS BASED ON REPLICA-EXCHANGE UMBRELLA SAMPLING II: FREE ENERGY ANALYSIS

2005 ◽  
Vol 04 (02) ◽  
pp. 433-448 ◽  
Author(s):  
KATSUMI MURATA ◽  
YUJI SUGITA ◽  
YUKO OKAMOTO
Keyword(s):  
Free Energy ◽  
Energy Analysis ◽  
Umbrella Sampling ◽  
Potential Of Mean Force ◽  
Sequence Dependence ◽  
Reaction Coordinates ◽  
Energy Profiles ◽  
Dynamics Simulations ◽  
Free Energy Analysis ◽  
Good Agreement

The free energy change of the stacking process of DNA dimers has been investigated by potential of mean force (PMF) calculations. Two reaction coordinates were considered. One is the distance R between the glycosidic nitrogen atoms of the bases. The other is the pseudo dihedral angle X (N–Cl′–Cl′–N) . All 16 possible DNA dimers composed of the adenine, cytosine, guanine, or thymine bases in 5′ and 3′ positions were considered. From the free energy profiles, we observed good stacking for all DNA dimers and sequence-dependent stacking stability. This sequence dependence of the stacking free energy is in good agreement with the experimental results. We also observed that the PMF is the lowest at R = 4.0~4.4 Å and X = 20~40° for all the DNA dimers except for the dGpdA dimer. These values are close to those of the canonical B-DNA (4.4 Å and 29°).

scholarly journals A Computational Protocol Combining DFT and Cheminformatics for Prediction of pH-Dependent Redox Potentials

2021 ◽  
Author(s):  
Rocco Peter Fornari ◽  
Piotr de Silva
Keyword(s):  
Organic Molecules ◽  
Ph Value ◽  
Computational Cost ◽  
Legendre Transform ◽  
Good Prediction ◽  
Redox Potentials ◽  
Free Energies ◽  
Hybrid Functional ◽  
Data Set ◽  
State Changes

<p>We present and validate a robust procedure to calculate the redox potentials of organic molecules at any pH value, using widely available quantum chemistry and cheminformatics methods. Using a consistent experimental data set for validation, we explore and compare a few different methods for calculating reaction free energies, the treatment of solvation, and the effect of pH on redox potentials. We find that the B3LYP hybrid functional with COSMO solvation method, in conjunction with thermal contributions evaluated from BLYP gas-phase harmonic frequencies, yields a good prediction of pH=0 redox potentials at a moderate computational cost. To predict how the potentials are affected by pH, we propose an improved version of the Alberty-Legendre transform that allows the construction of a more realistic Pourbaix diagram by taking into account how the protonation state changes with pH.</p>

scholarly journals Comparing alchemical and physical pathway methods for computing the absolute binding free energy of charged ligands

2018 ◽  
Vol 20 (25) ◽  
pp. 17081-17092 ◽  
Author(s):  
Nanjie Deng ◽  
Di Cui ◽  
Bin W. Zhang ◽  
Junchao Xia ◽  
Jeffrey Cruz ◽  
...  
Keyword(s):  
Free Energy ◽  
Binding Free Energy ◽  
Potential Of Mean Force ◽  
Free Energies ◽  
Decoupling Method ◽  
The Absolute ◽  
Absolute Binding Free Energy ◽  
Binding Free Energies ◽  
Charged Ligands

We compare the performance of the potential of mean force (PMF) method and double decoupling method (DDM) for computing absolute binding free energies for charged ligands.

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