Ground state structure
Posted: Thu May 13, 2010 12:40 pm
Hi All:
I was trying to calculate the ground state structure of a system. For this I first optimized the ENCUT and KPOINTS. I then moved on to relax the structure by ISIF = 2 ( relax ionic position), ISIF = 7 ( relax volume) and after reaching a minimum I used ISIF = 5 (shape relax). I repeated the cycle again. Please see the table below:
ISIF EGY, eV MAX. FORCE, eV/Ã… Total Force PR. kBar
2 -141.239874 0.0431 0.0462 -16.53
7 -141.253209 0.1287 0.0124 -1.54
2 -141.202352 0.0191 -0.0967 -7.27
7 -140.766275 1.4747 -0.1111 -0.64
2 -141.036644 0.059346 -0.0120 -1.14
7 -141.036981 0.06 1.54
2 -141.033040 0.0460 -0.008 -0.18
7 -141.033025 0.044 -0.009 -0.38
2 -141.033298 0.019 0.0585 -0.01
2 -141.033630 0.008 0.0540 0.04
2 -141.033748 0.0007 -0.0128 0.89
2 -141.033749 0.00037 -0.0131 0.05
5 -141.034513 0.08377 0.0687 2.37
7 -141.031489 0.073 0.0632 0.02
2 -141.031834 0.0292 0.0521 -1.04
7 -141.032134 0.032 0.0653 1.03
2 -141.029095 0.011 0.0838 0.25
7 -141.029072 0.008 0.078 -0.03
4 -141.029072 0.008 0.078 -0.03
2 -141.029657 0.0004 0.0253 -0.16
7 -141.029658 0.001 0.0253 0.03
2 -141.029233 0.001 0.0256 -0.01
7 -141.029233 0.0009 0.0258 0.00
7 -141.027872 0.001 -0.0287 0.05
Now, when I relax the shape of the cell, the total energy decreases but the maximim force on ion increases. But, if I want to achieve (almost) zero force and zero pressure on the system (ground state) the energy is not minimum (as you see in the table). So my problem is which structure should I consider as the ground state structure. I shall be thankful if any one can throw some light in this.
Thanks in anticipation
<span class='smallblacktext'>[ Edited ]</span>
I was trying to calculate the ground state structure of a system. For this I first optimized the ENCUT and KPOINTS. I then moved on to relax the structure by ISIF = 2 ( relax ionic position), ISIF = 7 ( relax volume) and after reaching a minimum I used ISIF = 5 (shape relax). I repeated the cycle again. Please see the table below:
ISIF EGY, eV MAX. FORCE, eV/Ã… Total Force PR. kBar
2 -141.239874 0.0431 0.0462 -16.53
7 -141.253209 0.1287 0.0124 -1.54
2 -141.202352 0.0191 -0.0967 -7.27
7 -140.766275 1.4747 -0.1111 -0.64
2 -141.036644 0.059346 -0.0120 -1.14
7 -141.036981 0.06 1.54
2 -141.033040 0.0460 -0.008 -0.18
7 -141.033025 0.044 -0.009 -0.38
2 -141.033298 0.019 0.0585 -0.01
2 -141.033630 0.008 0.0540 0.04
2 -141.033748 0.0007 -0.0128 0.89
2 -141.033749 0.00037 -0.0131 0.05
5 -141.034513 0.08377 0.0687 2.37
7 -141.031489 0.073 0.0632 0.02
2 -141.031834 0.0292 0.0521 -1.04
7 -141.032134 0.032 0.0653 1.03
2 -141.029095 0.011 0.0838 0.25
7 -141.029072 0.008 0.078 -0.03
4 -141.029072 0.008 0.078 -0.03
2 -141.029657 0.0004 0.0253 -0.16
7 -141.029658 0.001 0.0253 0.03
2 -141.029233 0.001 0.0256 -0.01
7 -141.029233 0.0009 0.0258 0.00
7 -141.027872 0.001 -0.0287 0.05
Now, when I relax the shape of the cell, the total energy decreases but the maximim force on ion increases. But, if I want to achieve (almost) zero force and zero pressure on the system (ground state) the energy is not minimum (as you see in the table). So my problem is which structure should I consider as the ground state structure. I shall be thankful if any one can throw some light in this.
Thanks in anticipation
<span class='smallblacktext'>[ Edited ]</span>