Ru slab optimization

[Lakshmi Anil]

Dear all,

I was trying to do geometry optimization of the 4x4 slab model of Ru(0001). The job was completed within 3 hours. Unfortunately, the slab structure distorts. One row of atoms from the top and bottom layers is moved to the middle layers. I also tried to do optimization by increasing the vacuum but the result was in the same way. Could anyone please help me how to resolve this problem? I am also attaching the input and output files of the optimization. 

[Lucas Lodeiro]

Hi,

recently I worked with the same system without problems, so I guess the problems are in the input. As I see, there are two main errors. First an EPS_SCF 1.0E-3 it is completely useless, your wavefunction neither the energy are converged at all, so the computed forces are completely wrong. As a general rule I use an EPS_SCF value equal to the square root of EPS_DEFAULT, and usually I reduce the EPS_DEFAULT value from the default one (1.0E-10) to 1.0E-12.

Secondly, your cell is ill defined. Ru(0001) is hexagonal shaped so there is a 120° between A and B vectors, and your input corresponds to a square one.

Also there are some issues in your computation: You use UKS in a non magnetic material, which enhances the computational time a lot, use RKS instead. The wavefunction guess is atomic for all geometries, it is better to use the converged one from the last geometry computed to save time. 

As advice, maybe you need to use more layers, I use 8 layers and everything works pretty well. Also for converged results using a bigger surface, you used a 4x4 surface, in my benchmark I found 6x6 is better. But obviously this enhance the computation time... Your vacuum (around 20 Angstroem) is enough for non charged and polarized surfaces.

Regards - Lucas Lodeiro

El mar, 16 ene 2024 a las 17:52, Lakshmi Anil (<lakshmi...@gmail.com>) escribió:

Dear all,

I was trying to do geometry optimization of the 4x4 slab model of Ru(0001). The job was completed within 3 hours. Unfortunately, the slab structure distorts. One row of atoms from the top and bottom layers is moved to the middle layers. I also tried to do optimization by increasing the vacuum but the result was in the same way. Could anyone please help me how to resolve this problem? I am also attaching the input and output files of the optimization. 

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[Lakshmi Anil]

Thank you, Lucas. I will make changes to my input and will try to run the simulation.

Kind regards,

Lkahsmi.

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