16
General Questions and Answers / Re: Pressure induced Enthalpy Calculation
« on: May 19, 2017, 08:05 »
I did all calculations by constraining Bravais lattice during optimization.
Guide me please
Guide me please
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17
General Questions and Answers / Re: Pressure induced Enthalpy Calculation
« on: May 18, 2017, 13:35 »
Yes Sir
18
General Questions and Answers / Pressure induced Enthalpy Calculation
« on: May 18, 2017, 11:24 »
Sir
By applying different pressure on a crystal structure i have calculated different Enthalpies at those pressure. I am getting a linear response upto a certain pressure(which is correct) but after that it is becoming zig zag.How can i rectify the problem?
By applying different pressure on a crystal structure i have calculated different Enthalpies at those pressure. I am getting a linear response upto a certain pressure(which is correct) but after that it is becoming zig zag.How can i rectify the problem?
19
General Questions and Answers / Re: DOS CALCULATION ERROR
« on: May 8, 2017, 19:37 »
Thank you so much Sir.. 
20
General Questions and Answers / DOS CALCULATION ERROR
« on: May 8, 2017, 09:50 »
Sir
I run a DOS calculation on the given script given below . I got an error which is in the log file. Please point me out the mistakes. Is it the problem with memory.? I have run a similar script with 25p.c Aluminium calculated with a different Density cut -off and in that, there is no error.
I run a DOS calculation on the given script given below . I got an error which is in the log file. Please point me out the mistakes. Is it the problem with memory.? I have run a similar script with 25p.c Aluminium calculated with a different Density cut -off and in that, there is no error.
21
General Questions and Answers / Re: Calculation using Primitive cell or Conventional Cell
« on: February 9, 2017, 12:43 »
Thanks for the reply
As advised ,
I performed optimization of the ZnGa2Te4 crystal taking density cut_off as 100 Hartree ( also in attached input file:opt-4) and 200 Hartree ( also in attached input file :opt-5) respectively each for 13*13*13 k_point sampling and even included Gamma point for both the optimization. The first optimization (with 100 Hartree) gives a=6.006947 angstrom and c=12.053359 angstrom, and the latter(with 200 Hartree) gives a=6.006978 angstrom, and c=12.052855 angstrom. The lattice parameter 'a' changes from a= 5.964880 Angstrom as in my previous optimization (earlier posted in the same Subject) even the parameter c also changes. Nevertheless these are far from the experimental values(a=5.92 angstrom and c=11.8 angstrom) . So what can be done to achieve a better optimization. Do basis sets also matters ? I have used SGI5 pseudopotential with the HIGH basis sets.
Another thing which I have mentioned in my earlier post that the space group changes from 82 to 1 after optimization. Does it should? If yes, then Why it changes?
Please guide me.
As advised ,
I performed optimization of the ZnGa2Te4 crystal taking density cut_off as 100 Hartree ( also in attached input file:opt-4) and 200 Hartree ( also in attached input file :opt-5) respectively each for 13*13*13 k_point sampling and even included Gamma point for both the optimization. The first optimization (with 100 Hartree) gives a=6.006947 angstrom and c=12.053359 angstrom, and the latter(with 200 Hartree) gives a=6.006978 angstrom, and c=12.052855 angstrom. The lattice parameter 'a' changes from a= 5.964880 Angstrom as in my previous optimization (earlier posted in the same Subject) even the parameter c also changes. Nevertheless these are far from the experimental values(a=5.92 angstrom and c=11.8 angstrom) . So what can be done to achieve a better optimization. Do basis sets also matters ? I have used SGI5 pseudopotential with the HIGH basis sets.
Another thing which I have mentioned in my earlier post that the space group changes from 82 to 1 after optimization. Does it should? If yes, then Why it changes?
Please guide me.
22
General Questions and Answers / Re: Calculation using Primitive cell or Conventional Cell
« on: February 8, 2017, 12:18 »
expt. value of c= 11.8 Angstrom
23
General Questions and Answers / Re: Calculation using Primitive cell or Conventional Cell
« on: February 8, 2017, 12:16 »
Thanks for the reply.
Sir,
I built a ZnGa2Te4(Space Group-82) crystal with the atomic positions as provided in the paper- http://www.sciencedirect.com/science/article/pii/S0025540816306730 . I tried to optimize the primitive cell using ATK-DFT using GGA-PBE exchange correlation and the pseudopotential SG15 with basis set High ( also in attached input file). So i start the optimization with 'a'=5.72 Angstrom c=13.043810 Angstrom ( expt. values a=5.92 and c=11.
.The optimization( Using OPTIMIZE GEOMETRY) was done without constraining any of the lattice vectors but the bravias lattice type was constrained to preserve the symmetry. It was completed and i got an optimized lattice parameters a= 5.964880 Angstrom and c=13.043810 Angstrom. Though 'a' value is close to the expt. value but 'c' value is quite far . Unexpectedly, the space group of the optimized structure is 1 . It means the structure has not optimized correctly. So could you please tell me what could be the error?
Sir,
I built a ZnGa2Te4(Space Group-82) crystal with the atomic positions as provided in the paper- http://www.sciencedirect.com/science/article/pii/S0025540816306730 . I tried to optimize the primitive cell using ATK-DFT using GGA-PBE exchange correlation and the pseudopotential SG15 with basis set High ( also in attached input file). So i start the optimization with 'a'=5.72 Angstrom c=13.043810 Angstrom ( expt. values a=5.92 and c=11.
.The optimization( Using OPTIMIZE GEOMETRY) was done without constraining any of the lattice vectors but the bravias lattice type was constrained to preserve the symmetry. It was completed and i got an optimized lattice parameters a= 5.964880 Angstrom and c=13.043810 Angstrom. Though 'a' value is close to the expt. value but 'c' value is quite far . Unexpectedly, the space group of the optimized structure is 1 . It means the structure has not optimized correctly. So could you please tell me what could be the error?
24
General Questions and Answers / Re: Calculation using Primitive cell or Conventional Cell
« on: February 6, 2017, 16:13 »
Should i use the primitive cell for a tetragonal crystal structure during such a structural optimization? please advise
25
General Questions and Answers / Re: Calculation using Primitive cell or Conventional Cell
« on: February 6, 2017, 16:03 »
Thanks
I want to optimize a tetragonal crystal structure which has both lattice parameters 'a' and 'b' . By varying values of 'a' i want to plot the energy vs volume graph. Do i have to keep c/a ratio constant? if yes, why? please guide.
I want to optimize a tetragonal crystal structure which has both lattice parameters 'a' and 'b' . By varying values of 'a' i want to plot the energy vs volume graph. Do i have to keep c/a ratio constant? if yes, why? please guide.
26
General Questions and Answers / Re: Calculation using Primitive cell or Conventional Cell
« on: February 6, 2017, 15:03 »
One one question!! i want to optimize a crystal structure by plotting Volume vs Energy and find its equilibrium lattice parameters . do i have to use conventional or primitive.. please guide me
27
General Questions and Answers / Re: Calculation using Primitive cell or Conventional Cell
« on: February 6, 2017, 14:52 »
Thanks a lot
28
General Questions and Answers / Calculation using Primitive cell or Conventional Cell
« on: February 6, 2017, 10:58 »
Hi everyone,
I tried to find the bandstructure of a primitive cell and i got an expected result. But when i tried using a conventional cell of the same crystal, i got a different bandstructure and the bandgap. Furthermore , the brilioun zone route reduces to only two points G and X. Is it because the number of atoms increased??.Please explain. And which cell should we use (primitive/conventional) for calculation of properties?
I tried to find the bandstructure of a primitive cell and i got an expected result. But when i tried using a conventional cell of the same crystal, i got a different bandstructure and the bandgap. Furthermore , the brilioun zone route reduces to only two points G and X. Is it because the number of atoms increased??.Please explain. And which cell should we use (primitive/conventional) for calculation of properties?
29
General Questions and Answers / Re: Structural Optimization to find equilibrium Lattice parameters
« on: February 2, 2017, 17:23 »
Thank You Jess
30
General Questions and Answers / Structural Optimization to find equilibrium Lattice parameters
« on: February 2, 2017, 14:28 »
Hi everyone,
I am very new to DFT, and I want to calculate the equilibrium lattice constants of a tetragonal crystal system. The experimental lattice parameters are a=5.92 (angstrom) and c=11.8(angstrom). So, for plotting the total energy Vs Lattice constant graph, I vary the value of 'a' by a step of 0.02 Angstrom from 4.72 Angstrom to 6.12 Angstrom with a fixed value of c. But i am getting an increasing curve which has a minimum at 4.72 Angstrom which is far different from the experimental value and other theoretical values. Atomic positions are correct and the space group too. Should c/a ratio needs to be fixed while changing the values of 'a'?Please help .
I am very new to DFT, and I want to calculate the equilibrium lattice constants of a tetragonal crystal system. The experimental lattice parameters are a=5.92 (angstrom) and c=11.8(angstrom). So, for plotting the total energy Vs Lattice constant graph, I vary the value of 'a' by a step of 0.02 Angstrom from 4.72 Angstrom to 6.12 Angstrom with a fixed value of c. But i am getting an increasing curve which has a minimum at 4.72 Angstrom which is far different from the experimental value and other theoretical values. Atomic positions are correct and the space group too. Should c/a ratio needs to be fixed while changing the values of 'a'?Please help .
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