Questions tagged [thermodynamics]

Questions concerned with thermodynamics as related to systems in materials modeling.

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3 votes
1 answer
88 views

Is hexaamminecobalt(III) chloride thermodynamically stable in pure water?

It is often said that "while cobalt(III) per se is strongly oxidising, hexamminecobalt(III) chloride is stable, even in concentrated hydrochloric acid, due to the strong donor properties of the ...
1 vote
0 answers
23 views

Relationship between grand potential and free energy?

What is the fundamental relationship between grand potential and free energy? In other words, what assumptions need to be made in order to obtain the free energy equation rather than the grand ...
3 votes
1 answer
59 views

Grand potential vs. Gibbs free energy of adsorption for ab initio thermodynamics

I have seen descriptions of ab initio thermodynamics where the phase energy diagram for the oxidation of metal surfaces can be constructed in terms of minimizing the grand potential or the Gibbs free ...
4 votes
1 answer
65 views

How to assign a "Boltzmann weight"?

I would like to assign a "Boltzmann weight" i.e. $\exp(-E/kT)$ to interactions between particles based on the relative energies. But wouldn't the largest particle-particle energies have the ...
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6 votes
2 answers
176 views

How are diffusion coefficients calculated?

To support my laboratory result, I'm searching for an MD/statistical mechanics approach to predict translational diffusion coefficients in the liquid phase. I'm aiming to describe small peptides and ...
6 votes
0 answers
170 views

How to calculate the Gibbs free energy for a reaction?

I am trying to learn how to calculate Gibbs free energy for a reaction. Assuming a reaction for two-dimensional TMDCs: MoS2 (solid) + 2Se(gas) ---> MoSe2 (solid)+ 2S (gas) I can calculate the ...
5 votes
1 answer
139 views

How to estimate chemical potential at a temperature?

Fermi level is electron chemical potential at 0K and we can obtain it from DFT calculation. However, the chemical potential is dependent on temperature. But I only find the equation for gas or simple ...
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4 votes
1 answer
50 views

COSMO Model and Electric Potential on the Surface of the Cavity Inside Perfect Conductor

I am learning about COSMO model used in chemical engineering for calculating chemical potential and similiar quantites (actitvity coefficients) for solutes in solutions/mixtures. In the model, it is ...
7 votes
0 answers
62 views

Sigma Profile in COSMO - RS model

As far as I understand, sigma profile in COSMO - RS is a probability distribution of screening charge density for certain molecular surface segment. In COSMO - RS, molecular surface area is segmented ...
5 votes
0 answers
45 views

How to derive specific heat of a crystalline material from phonon density of states? [closed]

I have done a simulation of a crystalline material using DFT and have extracted its normal modes and its phonon density of states. Does anyone have an algorithm/code or a detailed resource that can ...
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3 votes
0 answers
203 views

What input setting in Quantum ESPRESSO will allow me to calculate the free energy of a solid? [closed]

I understand that it's possible to calculate the Gibbs free energy of a system ab initio, see for example: How can we calculate the Gibbs free energy from first principles? I'm wondering how I can do ...
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7 votes
0 answers
244 views

Contribution in action from collisions for a gas?

So if I write the action for a gas: $$ S = \int (T -U) dt \tag{1}$$ where $T$ is the kinetic energy and $U$ is potential energy. I suspect there is a constant term (which does not affect the equations ...
10 votes
1 answer
336 views

How reactivity of a organic molecule depends upon HOMO and LUMO

I am studying the dehydrogenation of an organic molecule. I see the HUMO-LUMO gap remains nearly the same for many dehydrogenated steps (for some steps, it is exactly the same) while the position of ...
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5 votes
0 answers
75 views

What is the qualitative meaning of the Nosé thermostat?

The Nosé thermostat is explained in Chapter 6 of Understanding Molecular Simulation. Perhaps it's because I find it difficult to follow the derivation, but the physical meaning behind the $s$ ...
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8 votes
1 answer
155 views

Functional derivatives in DFT

Crossposted from Physics SE. I am studying density functional theory and I am currently dealing with manipulating the intrinsic free energy, $\mathcal{F}$, which is defined as $$\mathcal{F} = F - \int ...
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17 votes
2 answers
939 views

Flying ice cube effect in molecular dynamics?

I am trying to understand what exactly the flying ice cube effect is, and how it manifests itself in MD simulation. From what I have read about it, I see that as we run certain forms of velocity-...
  • 3,957
7 votes
1 answer
254 views

Can the dehydrogenation energy be negative?

I am studying the dehydrogenation of a cyclohexane ring containing $\ce{B-N}$ on the adjacent position. or simply we can think about $\ce{H3N-BH3}$. If we release one $\ce{H2}$ molecule from it then ...
  • 1,643
10 votes
1 answer
157 views

Is it possible to experimentally verify this collision rate formula?

Background Let's say I have the $i$'th gas molecule with velocity $\vec v_i(t)$ at time $t$. To find the net displacement $s_i$ we integrate with respect to $t$: $$ \vec s_i = \int_{0}^{t} \vec v_i(t')...
8 votes
1 answer
134 views

Should I add vdW interaction to estimate chemical potential of metallic elements?

I am considering layered oxides $\ce{LiCoO2}$. Previous papers suggested that vdW interaction should be added to get lattice parameters closer to experimental data. I would like to dope other elements ...
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8 votes
1 answer
128 views

If a molecule's theoretical formation energy is positive, can it still be synthesized?

I have designed a molecule using hydrocarbons A and B. I am getting the formation energy slightly positive (~0.04 eV). As per my experience, any positive formation energy means that the designed ...
  • 1,643
6 votes
1 answer
77 views

Is it possible to analytically solve for a particular phase region of a CALPHAD database? (instead of guessing and checking)

As I understand it, a given CALPHAD database is essentially just a set of equations that model the Gibbs free energy of each phase within a given alloy system (set of elements). Typically, the main ...
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4 votes
2 answers
87 views

CASSCF and thermochemistry—effect of excited determinants on rotational and vibrational modes

So this question is linked to the other question I asked about the electronic patition function and CASSCF. When calculating thermochemical data (e.g. Gibbs Free energy) the partition functions are ...
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4 votes
1 answer
119 views

Excited determinants, electronic partition function and thermochemistry calculation

While studying statistical thermodynamics I came across the partition functions, which connect the quantum world to the macroscopic world. I understand that partition functions are used to calculate ...
  • 5,834
6 votes
1 answer
198 views

Thermo-calc: Calculate precipitation driving force by parallel tangent construction

I want to calculate the difference in Gibbs free energies between a Zr-Cu-Al liquid (composition - Zr 65 Cu 27.5 Al 7.5 at%) and the CuZr2 solid phase as a function of temperature (300 - 1000 K). In ...
11 votes
1 answer
776 views

Selection of appropriate Langevin damping parameter for MD of solid metal

I am performing an MD simulation involving solid metal. The system is in the NVT ensemble, and I am using the Langevin thermostat (fix Langevin in LAMMPS) to enforce this. I have previously used the ...
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3 votes
0 answers
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Doubt in Raoultian and Henrian Standard State [closed]

$Si(liq)=Si_\text{(1 wt% Fe)}$ Can you describe what is going on here?All that they ask for is change in Gibbs free energy for the process.I am completely unable to figure why this particular model is ...
7 votes
1 answer
81 views

High accuracy energy methods, are they worth it?

I'm trying to figure out for myself the necessity of high-accuracy compound methods for energy like W1 or Gn families. I'm learning computational chemistry by myself and sometimes lack systematical ...
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9 votes
1 answer
500 views

Why is specific heat not zero at absolute zero?

In this old paper on Monte Carlo simulations of Lennard-Jones solid, specific heat behaviour (both $c_p$ and $c_v$) have been reported. As you can see from the picture below, both $c_p$ and $c_v$ goes ...
11 votes
1 answer
226 views

How to get order constitution data for single equilibrium calculation in Thermo-Calc's TC Python module?

I know that it is possible to get order constitution data for phases when using Thermo-Calc's GUI (e.g. to get "BCC_B2 DISORD" instead of just "BCC_B2") for a single equilibrium ...
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7 votes
1 answer
113 views

For ergodicity, what is the significance of the R value and slope?

I am calculating MSDs for the first time and have been struggling to find newbie-level resources on understanding them. If anyone could please suggest any resources or provide guidance on how to ...
  • 707
6 votes
0 answers
128 views

Why does Thermo-Calc one axis equilibrium calculation get stuck in never ending loop? [closed]

I've been trying to run a Thermo-Calc one axis equilibrium calculation on some quaternary alloys in the TCHEA4 database. Most of the calculations work fine, but for some alloys it gets stuck in a loop ...
  • 621
9 votes
1 answer
209 views

For a Thermo-Calc database, is it possible to view the equation/parameters of the Gibbs free energy models?

I want to get the equations that model free energy for a given phase in a given alloy system (see attached image). I do not just want to get values of free energy for specific compositions. Is it ...
  • 621
10 votes
1 answer
121 views

Correcting thermodynamic data for concentration, what concentration is best to use?

In computational chemistry when using transition state theory we often use standard states for all involved structures. However, sometimes people argue that it should be corrected for concentration (...
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11 votes
1 answer
276 views

How does one compute the boiling point of a liquid made of a particular molecule?

This question is in relation to Anomalous boiling point of "iso-" alkanes on Chemistry SE. I want to compute the boiling point of the different isomers of an n-carbon alkane to check what ...
16 votes
1 answer
272 views

Is there any reason not to sum the kinetic and potential energy from an NPT simulation to get internal energy?

I would be very grateful for some newbie-level advice from a thermodynamics guru. I ran NPT simulations on a particular system (in CP2K software) to get fluid densities for use in fluid dynamics ...
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11 votes
1 answer
265 views

Are there any MD packages that do proper free energy sampling in the NPT ensemble?

Statistical Mechanics is the basis of molecular level calculations of properties and averages. Nowadays free energy calculations are fairly "turn-the-crank", which is not necessarily a good ...
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18 votes
1 answer
527 views

What are the ways to ensure thermodynamic stability of a DFT modelled new structure?

One way of predicting the thermodynamic stability of a DFT modelled structure is to calculate the energy above convex hull, which was used as the criterion in The Materials Project database. For ...
8 votes
1 answer
119 views

What contributes to the total enthalpy of a system?

This answer refers to a paper that calculates $\Delta H$ as $\Delta E_{\textrm{electronic}} + \Delta E_{\textrm{vibrational}}$. However, what if I had enough computing power, and I wanted to get the ...
12 votes
1 answer
174 views

What are the methods for calculating solvation effects in free energies and how do they compare?

I've just found this paper (J. Chem. Phys. 141, 174106 (2014)) that deals with the translational and rotational entropies in solution. The method is promising but, unfortunately, requires a ...
16 votes
1 answer
330 views

How to calculate t-zero temperature using Thermo-Calc- Python (TCPython) for multiple alloys?

T-zero temperature is the temperature at which the Gibbs energies of two phases are equal. Here, I wish to find the temperature at which FCC and BCC have same Gibbs energy. Thermo-Calc console mode ...
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14 votes
3 answers
132 views

What thermodynamic data is collected in order to build a CALPHAD model?

To build a model using the CALPHAD approach, i.e. Gibbs free energy as a function of composition and temperature, typically taking the form of a Redlich-Kister polynomial, what kind of thermodynamic ...