[QE-users] some questions about cpmd in quantum espresso

[杨庆]

Dear qe users,
       I am calculating the CPMD of iron oxide, but I have encountered many problems in the calculation process. I hope you can give me some suggestions. The questions are as follows:


1. In the manual of cp.x module, I see that if the force of each atom is less than 0.1au, there is no need to do ion relaxation. If it is greater than 0.1au, the structure may be destroyed in the later calculation process, and my structure is indeed destroyed in the nose process. Here, I want to ask how to test the atomic force of the initial structure in cp.x?


2. My structure is damaged. Besides excessive force, can it be caused by other factors? For example, the choice of cutoff energy, electronic mass, and time step. My truncation energy is selected according to the pseudopotential, with an electron mass of 400au and a time step of 5au For the reason that the force may be too large, I try to use ion_ dynamics = 'damp',ion_ Damping = 0.05, but it can't reach the set value of forc_ conv_ thr and the maximum value of atomic force fluctuate greatly. How can I solve this?


3. When I only have different pseudopotentials and other parameters are the same, I find that the value of pressure in the output energy file is quite different. When I use Fe pbe-sp-van_ak. UPF, the pressure is about 5Gpa, while when I use Fe pbe-n-rrkjus_ psl. 1.0.0. UPF, the pressure is about 100GPa. What is the possible reason for this?
Looking forward to your reply!Thank you！
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