Molecular Dynamics Part 3 - Elastic constants , Melting , Phase transition Solid to Liquid
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- เผยแพร่เมื่อ 26 ก.ย. 2024
- Calculation elastic constants using Molecular dynamics , Melting of Copper, Phase transition solid to liquid , isothermal elastic constants
why you have chosen the 0K value of Cijkl to calculate the born term i.e second derivative of potential energy with respect to stain as their in other paper people of calculated the born term at the finite temperature? please give some thought on it.
The script for elastic constants at 0K is part of the LAMMPS PACKAGE under the Folder EXAMPLES . They also have a script for calculations at a Given Constant Temperature . but i want to calculate for pure magnesium at 0K to its melting point, i am finding that the elastic constant is fluctuating for the same, but in experimental it was decreasing. can you comment on that?
The LAMMPS script calculates the elastic constants by slightly deforming each of the six independent terms on the strain tensor and observing the internal energy change (2nd derivative) or the 1st derivative of stress with respect to strain. The previous method is sensitive to the epsilon (strain). Therefore, you may need to play around to find the optimal epsilon.
Copper is an FCC structure, and the shear modulus equals the constant C44. You can predict the solid to liquid transition (melting) by observing the change in the shear; as for liquids, the shear is zero. I'm not sure if such is the case for Magnesium.
you may read :
INFLUENCE OF POINT DEFECTS ON THE SHEAR ELASTIC COEFFICIENTS AND ON THE MELTING TEMPERATURE OF COPPER
AMIT KANIGEL, JOAN ADLER, and EMIL POLTURAK
Department of Physics, Technion-IIT, Haifa 32000, Israel
www.worldscientific.com/doi/10.1142/S0129183101001900
great job..
Hi, can you send the elastic constant script again? Actually, the old link is not working.
Please reshare the link for script. the links given already aren't working.
And sir also the script to find at afinite temperature . Sir is this valid for all type of crystals?
The link is here drive.google.com/drive/folders/1FWxHQ_1jyO8DtCaYhAROopUhbgVHj4bF?usp=sharing
@@oscarguerrero4584 thank you
sir can you pls give the script to find the elastic constants at zero K ,the link is not working
Please can you help with a Lammps script that calculate average elastic constant, I have my dumps files but I don't know how to get the elastic constant
What dump files you exactly have ? You need the stress fluctuations to calculate the Elastic constants at a given Temperature
Thank Oscar, i was able to do it, can you help me with the files for elastic constant with temperature including the octave file thanks
Daramola, not offense, but I'm not going to look at your script. I'm already retired and it does required a lot of brain effort . However, Just quickly tell me what are the steps your planning to do and I will provide you feedback . What dump files you exactly have and how you obtained them ? I do want to help you. Let me see around if I can find few references on my Drive about Elastic constants at finite temperature
@@oscarguerrero4584 I want to calculate the elastic constant of Iron-Chromium at 300k
@@daramolaayobami6197 , Please read these references : 1drv.ms/u/s!AtTZsJPQUFDVgYowW2-j8FZ9TwhtcQ?e=9GFggM
MY question was more related about the steps to find the solution. I dont really care the name of the alloy . Are you using periodic boundary conditions, NVT or NVE ? what your dump file's data contain ?
Will this be work for HCP crystal, if possible please share the formulation.
what will work?
This method and formulation
@@sauravsingh1689 Yes it should work . The calculation of the elastic constants is based on the stress fluctuations
@@oscarguerrero4584 one more thing can you elaborate how this 160.2 come into picture.
@@SauravKumarPME Pressure: 1 eV/Angstrom 3 = 160.21766208 GPa. Using LAMMPS unit metal the Volume is on Angstrom^3 and the temperature is Kelvin. I'm using here KB = 8.617333262145*(10^(-5)) # eV/K . Please read these references: 1drv.ms/u/s!AtTZsJPQUFDVgYowW2-j8FZ9TwhtcQ?e=9GFggM
Please I need the script for 0K Elastic constant and 300k
The script for elastic constants at 0K is part of the LAMMPS PACKAGE under the Folder EXAMPLES . They also have a script for calculations at a Given Constant Temperature . However, I don't recommend using the brute force method of applying a small deformation in the 6 directions and using the derivative of the Stress/strain or 2nd derivative of the Energy/strain at a Given T . The link to the script is here : 1drv.ms/u/s!AtTZsJPQUFDVgYonVut3uk42druCfg?e=VkFb0Z
@@oscarguerrero4584 thanks, I am trying to get elastic constant for Edge mobility dislocation of an Alloy at 0K, is it possible to use this method, also can i get yout octave script for post processing
@@daramolaayobami6197 , How the elastic constants relate to the mobility of the dislocation ? Well it kinda does make sense , if we consider the Elastic/stiffness constants being the resistance to stretching/compressing . All 3 methods are valid , as a rule of thumb you start at 0K and then you try at a given constant temperature . Why not calculating the gamma surface energy at preferential directions (slip plane) to predict the mobility of the dislocation ?
@@oscarguerrero4584 yes, I was planning on taking the average elastic constant to determine C11, C12 and C44 but it's a bit complex for me. Please can you attach your octave code maybe it may help me, because I use your code at 0K for three alloy elements it gave me a wrong answer compare to the experimental result I am following
@@oscarguerrero4584 hello Oscar, on above-given link there is nothing showing this message (This item might not exist or is no longer available
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I want to calculate elastic constants of BCC molybdenum, can you please share the LAMMPS code with me to calculate elastic constants for Molybdenum, please?