Messages

1

General Questions and Answers / Re: Elastic constants of a disordered rocksalt

« on: May 14, 2019, 12:34 »

               After calculation, I got 21 independent elastic constants (bcoz symmetry was not detected by the tool).
 Are saying that from 21 elastic contants, I have to ignore the zero component of the particular crystal system and to take the average of the equal components?

 

2

General Questions and Answers / Re: Elastic constants of a disordered rocksalt

« on: May 8, 2019, 09:29 »

For an amorphous material, the symmetry is much lower than that for an ordered phase, or very likely there is no point symmetry, so that you will have to calculate all the elastic constants, assuming no symmetry for your amorphous structure.

If you think that the symmetry is approximately preserved (or you want to enforce it) for the amorphous structure, you may do averaging (in a post-processing manner) over the elastic constants that are supposed to be identical for the ordered material. In this case, you will get three effective elastic constants.

My question is how to perfrom averaging ...Can u give some references??

3

General Questions and Answers / Re: How much memory will it require to run the script?

« on: February 15, 2018, 12:13 »

Yes it hung up and didn't give any error.

4

General Questions and Answers / How much memory will it require to run the script?

« on: February 15, 2018, 07:07 »

           I am trying to run a script. How much memory will it require? The calculation unfortunately stops in the middle.

5

General Questions and Answers / Re: Phase Transition Pressure

« on: September 20, 2017, 11:31 »

Thank you Sir

6

General Questions and Answers / Phase Transition Pressure

« on: September 20, 2017, 08:58 »

Hello everyone,
               1. How does the  common tangent drawn between Energy-Volume Curves of two phases of the same compound give the transition pressure between the two phases thermodynamically?
               2.  I  read that the slope of the tangent  gives the transition pressure. The steeper the slope, the transition pressure becomes smaller. What is the relationship between the slope of the common tangent and the transition pressure in GPa?

7

General Questions and Answers / Re: Prediction of a strucure

« on: September 11, 2017, 14:28 »

Thank you Sir ,
        I will be trying that

8

General Questions and Answers / Re: Prediction of a strucure

« on: September 11, 2017, 13:06 »

Thank you sirs for the replies.
  If i do geometry optimization of the structure, should i preserve the symmetry (by constraining  bravais_lattice) or should i perform unconstrained?

9

General Questions and Answers / Prediction of a strucure

« on: September 10, 2017, 22:28 »

Sir
      I have experimental lattice parameters of a structure at 12 GPa (stable at this pressure)  . How can i model the structure at 0 GPa from the above information?

10

General Questions and Answers / Space Group Change after creating a defect compound

« on: September 7, 2017, 08:27 »

Sir ,
       To model a defect compound (disordered rocksalt), i used repeat cell . I found that after building the structure with  vacancies involved , the space group changes .
      1. Will this change not affect the results of any calculation ?
     2. If elastic constants are calculated, how to analyse the result if there are more independent elastic constants than the rocksalt structure?

11

General Questions and Answers / Phase transition

« on: September 6, 2017, 15:54 »

Sir
       I want to study pressure induced phase transition of a defect chalcopyrite (low pressure phase). The high pressure phase is a disordered structure with fractional occupancy of atoms ( for this i want to build using supercell 2X2X2). More importantly, I want to calculate the transition pressure  between the two phases.
1.  In order to do this, do i have to build a supercell of the same size for the low pressure phase to compare the enthalpies with the high pressure phase and predict the required transition pressure ?
2. For this, do i have to use LDA or GGA?

12

General Questions and Answers / Keeping script in Queue

« on: May 31, 2017, 20:00 »

Sir
     Is it possible to keep a script in queue while  other script is running and just after the job is completed the script in queue automatically starts
running?

13

General Questions and Answers / Relation between Pressure applied and Density Mesh cut-off

« on: May 24, 2017, 12:40 »

Hello  sir
               Is there any relationship between pressure applied to a configuration and the mesh cut -off? Please explain

14

General Questions and Answers / Re: Pressure effect

« on: May 24, 2017, 12:31 »

Ok sir i got the answer .
     Thank you

15

General Questions and Answers / Pressure effect

« on: May 23, 2017, 08:56 »

hello Sir
      By applying different pressure on a crystal structure i have calculated different Enthalpies at those pressure(Using OptimizeGeometry Block). 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? I am using the same Density cut-off and k-pts