optimized EOS coordinates and final CVOLOPT

job314

Alessandro, I am having a blast finding the volume of the crystals using EOS which I can then use for supercell etc. I was wondering about the technically correct sequence here:

-I run EOS, it prints
SORTING VOLUMES/ENERGIES

 VOLUME (A^3)    ENERGY (a.u.)

 443.177886   -2.716943460865E+03
 451.049595   -2.716949077158E+03
 458.957263   -2.716952819603E+03
 466.951330   -2.716954739628E+03
 471.547619   -2.716955035989E+03
 475.033963   -2.716954889255E+03
 483.208420   -2.716953349891E+03
 491.475047   -2.716950220038E+03
 499.836229   -2.716945606438E+03

+++++++ FITTING USING ALL POINTS +++++++

USERS OF THIS EOS MODULE SHOULD KINDLY CITE THE FOLLOWING REFERENCE:

A. Erba, A. Mahmoud, D. Belmonte and R. Dovesi, J. Chem. Phys., 140, 124703 (2014)

EQUATION OF STATE VOL(A^3) E(AU) BM(GPa) BM PRIME

MURNAGHAN 1944 471.7053 -2716.95501994 53.34 3.41
BIRCH-MURNAGHAN 1947 471.7038 -2716.95502102 53.40 3.42
POIRIER-TARANTOLA 1998 471.7006 -2716.95502119 53.41 3.43
VINET 1987 471.7019 -2716.95502111 53.40 3.43

POLYNOMIAL FITTING VOL(A^3) E(AU) BM(GPa)

THIRD ORDER POLYNOMIAL 471.6937 -2716.95502707 53.73
FOURTH ORDER POLYNOMIAL 471.6893 -2716.95503729 54.28
FIFTH ORDER POLYNOMIAL 471.6651 -2716.95503712 54.28

Now, is there a trick to make software plots lattice parameters for that minimum volume? I could not find any

Since I could not find any, I take the two lattice parameters around that lowest energy volume and extrapolate lattice parameters to it. My second question then is - should I run one more CVOLOPT using that EOS lowest volume extrapolated lattice parameters to arrive to something that is not only lowest volume, but also optimal lattice parameters for that volume OR whatever comes out from EOS is already optimal lattice parameters for that minimal volume?

thank you

job314

Correction, I tried my last suggestion and, I do not understand why, volume changes when running CVOLOPT. The name implies that volume will be constant but it is not, it changes, which defeats the purpose of me wanting to keep volume fixed and finding the optimal lattice parameters for that volume

INFORMATION **** CVOLOPT **** CONSTANT VOLUME OPTIMIZATION