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16 votes
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Difference between potential energy, free energy and Coulomb energy in solid state physics

I can't answer in the context of DFT/VASP, where these terms might have specific uses, but I can offer some general comments. These terms are not necessarily mutually exclusive: Total energy probably ...
taciteloquence's user avatar
13 votes
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Is there any definitive evidence that implicit solvation methods are more accurate than explicit solvation methods for free energy calculations?

In principle, you would expect the exact opposite (i.e. explicit better than implicit) simply because an explicit model more closely matches the reality of molecules interacting with other molecules ...
Tyberius's user avatar
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12 votes
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Why are ions in water not paired?

There actually is ion pairing in aqueous solutions, but the concentration of paired ions is usually much lower than fully dissociated ions. You should also take into account that typical ...
Stephen's user avatar
  • 721
11 votes
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Can I compute the free energy difference in (temporally) nearby micro-states using the Zwanzig equation for Free Energy Perturbation?

As I have previously discussed with you, there is no such thing as frame-wise free energies, so the premise of your question is flawed. With this in mind, I think it would actually be useful to tell ...
Godzilla's user avatar
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10 votes

Is there any definitive evidence that implicit solvation methods are more accurate than explicit solvation methods for free energy calculations?

From what I have read, the performance of implicit models depends on a combination of the method used (Poisson-Boltzmann vs. Generalized-Born vs. another analytical method); and the size, shape, and ...
anneb101's user avatar
  • 995
9 votes

Calculating enthalpy of a chemical reaction using DFT

The main question here is whether the reaction is favourable or not, and for that we may need to go beyond the usual energies computed in a ground state DFT calculation, and consider the free energy. ...
Phil Hasnip's user avatar
  • 8,052
9 votes
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How to calculate Gibbs free energy of adsorption at constant temperature with varying pressures

IMO the equations you show use too many "$\Delta$" which makes it more confusing. I will hence try to avoid the use of "$\Delta$" in the equations below. To get the adsorption free ...
Shaun Han's user avatar
  • 1,930
8 votes

Calculate deprotonation energy or Gibbs free energy of acids

Despite the fact I'm not sure what your question is, I'll try to answer it :-) the energy of H+ derived from DFT should be zero The idea is that a pure $\ce{H+}$ ion exists in a gas phase only, ...
Ivan Chernyshov's user avatar
8 votes

Is there any definitive evidence that implicit solvation methods are more accurate than explicit solvation methods for free energy calculations?

Highly depends on what your system of interest is. (i) For molecular and ionic systems, check papers by Chris Cramer and Donald Truhlar. (ii) Another paper of interest for heterogeneous catalysis ...
gogo's user avatar
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8 votes
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Software for generating ensembles of dimer pairs of organic molecules

Generating all possible structures systematically might be difficult. When it comes to the generation and refinement of chemically useful structure guesses, I'd recommend looking into CREST by Stefan ...
Antimon's user avatar
  • 546
7 votes
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Water dimer and Free Energy Perturbation (FEP)

You are on the right track, but there are a few more details, typically. For one, for a FEP, we calculate the change over many windows. We generally also used soft-core potentials. Soft-core ...
B. Kelly's user avatar
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7 votes
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Should one consider the spatial degeneracies of the electronic state while calculating the Gibbs free energy?

First, let's look from the most fundamental point of view. For this part of the answer I'll be referencing McQuarrie's Statistical Mechanics [1]. As the Gibbs free energy, $G$, can be calculated from ...
Antonio de Oliveira-Filho's user avatar
5 votes
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Zero point correction and free energy calculation with imaginary modes?

The two most common approaches for dealing with imaginary frequencies in free energy computations are: Compute the free energy using only the modes with real valued frequencies Reoptimize the ...
Tyberius's user avatar
  • 15.6k
5 votes

How can I justify that in DFT entalphy is Gibbs free energy?

DFT is most commonly used to calculate minimized energy structures. This is likely what your project is on, unless you're doing ab initio molecular dynamics, or excited state DFT (e.g. time-dependent ...
Hayden S's user avatar
  • 940
4 votes

Gibbs free energy modification after finishing NEB?

I think the first question you have to ask is whether you can get an accurate free energy for your reaction barrier in VASP. If you have a reaction with a small molecule on an oxide surface under ...
lamycel's user avatar
  • 121
3 votes

What is the largest number of collective variables used in a metadynamics simulation?

This paper from 2015 describes a modified metadynamics method (parallel-bias metadynamics) by which the authors demonstrate enhanced sampling over six collective variables for the tryptophan cage ...
Shern Ren Tee's user avatar
3 votes

How to calculate phase regions using CALPHAD for higher order systems (>3 elements)?

I assume someone at TCSAB (which market Thermo-Calc) can answer this better but as I participated in developing TC a long time ago and now I work on a similar free software called OpenCalphad (I ...
Bo Sundman's user avatar
2 votes
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Gibbs free energy modification after finishing NEB?

To get the Gibbs Free energy from the internal energy, you have to consider the configurational entropy. I anticipate you need the Gibbs Free energy to calculate the activation barrier as a function ...
Tara Mishra's user avatar
2 votes

Gibbs free energy modification after finishing NEB?

It depends on why you've made the NEB. If to find a possible reaction coordinate, you can use the ∆E as an indicator. Another thing is that you can't perform the "traditional" ...
Andrea Pellegrini's user avatar
2 votes

How to estimate chemical potential at a temperature?

I guess the you are working on doping. Suppose in the following we consider only semiconductors. I disagree with "Fermi level is electron chemical potential at 0K and we can obtain it from DFT ...
Memories's user avatar
  • 353
2 votes

Why are ions in water not paired?

It's the entropy – suggested reading, ET Jaynes: Information theory and statistical mechanics. For the same reason, water vapour exists already at room temperatur (~1 mol/m³, TU Wien: Vapor Pressure ...
Rainald62's user avatar
  • 121
1 vote

Potential of mean force from potential energy

Your definition for "a potential of mean force" (or PMF) is not correct. The PMF of a probe from a reference particle is the potential energy change when the probe is moved towards or ...
Shern Ren Tee's user avatar
1 vote

What is the meaning of a "free energy per unit surface area" vs "pressure" plot?

The graph does show that at high pressures the $\Delta G$ per surface area values are lower, which would usually indicate stability. I agree with you that as the pressure goes lower, the stability ...
Nike Dattani - No Free Time's user avatar
1 vote

Relationship between grand potential and free energy?

The grand potential depend on T, the chemical potentials of the components and on V. The Gibbs energy (previously called Gibbs free energy) depend on T, P and the amount of the components. There is ...
Bo Sundman's user avatar

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