The ABINIT Users Mailing List ( CLOSED )

["Z.J." <kedypan@gmail.com>]

Dear Hamann,

    Thank you very much for your help. I know abinit can calculate the elastic tensor directly. But I want to know the calculating process of elastic constants in abinit. Would you give me some instructions on how to calculate the elastic constants by numerical differentiation? I don't know how to obtain the input data of the distorted structure. Please teach me to do this. Taking cubic structure as an example, the tetragonal train and the rhombohedral one are applied to the original cubic structure. Which vector of the original cubic structure, primitive lattice vector or conventional lattice vector, should be chosen to be multiplied by the train matrix? Comparing with the cartesian coordinates and fractional coordinates of the original structure, what will the cartesian coordinates and the fractional ones of the distorted structure change to? To my knowledge, the fractional coordinates do not change and only the cartesian coordinates do change. Is this Right? I am looking forward to your reply. Thank you very much for your help.

    Best regards.

                                                             Yours sincerely,

                                                             Jian Zhu

 

2006/11/30, D. R. Hamann <drhamann@mat-simresearch.com>:

Dear Jian,

Abinit can calculate the elastic tensor directly, giving the results in
Cartesian coordinates and standard units (GPa).  Work through the
tutorial "elastic properties" and you should be able to apply these
methods to your problem.  (If you haven't done so, be sure to work
through the basic tutorials first.)

From your questions, it sounds as if you intended to calculate the
elastic constants by numerical differentiation.  This is very tricky,
and it is very difficult to get accurate results this way, especially
for any structure with internal degrees of freedom.

Don Hamann

Z.J. wrote:
> Hi, dear all users,
>       I am so sorry to disturb you. I have some problems
> about the elastic constants calculations to turn to you for your
> help.My problems are as follows:
>      (1) Must the strain matrix be multiplied with the vector of the
> primitive cell? If the strain matrix multiplies with the conventional
> lattice vectors, could I obtain the right calculation results?
>      (2) Will both the Cartesian coordinates and the fractional (x,y,z) of
> atoms in the distorted primitive cell change after distortation? If they
> will change, how and what will they change?
>      (3) How to determine the space group of distorted primitive cell?
>
>      In all, the key point of the problem is how to obtain the input
> data of
> distorted lattice of crystal.
>
>      Thank you for your valuable and informative advice very much.
>
>      Best regards.
>
>     Yours sincerely,
>
>                                                Jian Zhu

--
D. R. Hamann
Mat-Sim Research LLC    | Deptartment of Physics
P.O. Box 742            |  and Astronomy
Murray Hill, NJ 07974   | Rutgers University
phone: 908-370-8079     | 732-445-4381

email: drhamann@mat-simresearch.com

-- 
School of Materials Science and Engineering
Shanghai Jiao Tong University
Kedy