<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:14pt"><div>Dear QE developers, <br>I have a question about optimization of a hcp structure (e.g. Ti and Zr).<br>Any hcp structure have two lattice constants (a and c), so for scf calculation, it is nessesry to optimize both lattice constants.<br><br><br>Method 1: Fixed celldm(3) at ideal c/a ratio (1.633) and then changed celldm(1)=a and eventually computation of total energy. <br><br>Method 2: Fixed celldm(1) at experimental lattice constant and then changed celldm(3)=c/a and computing of total energy.<br><br>Method 3: Fixed unit cell volume at experimental volume and then changed c/a ratio and calculation of a (Volume=fixed) and run scf <br><br>calculation with different a and c/a. <br><br><br>what is best method for optimization of a and c? Method 1, 2 , 3 or others method?<br><br><br>I am very thankful any to help
me.<br><br>--<br>Romeda Azeen,<br>Bhavnagar University Bhavnagar 364002 Gujarat India</div></div></body></html>