[Wien] find minimum

[Lawal Mohammed]

Dear Gavin Abo, Sir,

In line with the discussion above, I got when I plot E vs c/a the following

Fit of:  E = a1 + a2*x + a3*x^2 + a4*x^3 + a5*x^4
a1                    1.000
a2                     0.000    1.000
a3                    -0.761   -0.000    1.000
a4                    -0.000   -0.930    0.000    1.000
a5                     0.642    0.000    -0.972   -0.000    1.000   

In this case what should be the value for a2, a3, a4, and a5? 

Thank you in advance for your response.
With kind regards
Mohammed Lawal 





On Friday, January 24, 2014 7:08 AM, Gavin Abo <gsabo at crimson.ua.edu> wrote:
 
Below is a summary of previous posts that should help.

To plot energy vs b/a:

(a) You should be able to rename the scf files and then plot with
      the energy vs c/a option of eplot
[http://zeus.theochem.tuwien.ac.at/pipermail/wien/2009-January/012053.html].
(b) You could also plot energy vs b/a in another program like
      Origin
[http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg08841.html].

To get the optimized c/a (or b/a) value,  you can calculate it
      from the curve fit equation
[http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg05826.html].

An example calculation is given below.

When you plot E vs. c/a with eplot, you should get something like:

Fit of:  E = a1 + a2*x + a3*x^2 + a4*x^3 + a5*x^4
a1              = -2201.24
a2              = 0.00233422
a3              = 0.000188276
a4              = 1.33462e-05
a5              = 9.76521e-07

From dE/dx = 0, we get the equation:

a2 + 2*a3*x+3*a4*x^2+4*a5*x^3 = 0

Solving this equation for x, x = -7.7555, which is the optimized
      c/a ratio in %.  I got x with Octave, but there are other software
      programs that you can find on the internet to solve the polynomial
      equation.

Octave input:

dEdx = [4*9.76521e-07,3*1.33462e-05,2*0.000188276,0.00233422]
roots(dEdx)

Octave output:

  -1.2474 + 8.6889i
  -1.2474 - 8.6889i
  -7.7555 + 0.0000i  <= This polynomial root is chosen as x,
      because the imaginary part is zero and it appears in the energy vs
      c/a plot.

If you also want the minimum E, just plug the x value back into
      the curve fit equation and solve for E (= -2201.2495).

On 1/22/2014 7:22 AM, MAHDI SALMANI HIRMAND wrote:

Dear Prof. Blaha,
>Please let me know why there is not a program for finding minimum of c/a or b/a ratio with Wien2k Package when we optimize c/a or b/a.
>eplot program can show curve of Energy Vs. c/a but it doesn't find minimum of c/a.
>Please guide me
>With best
>Mahdi

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