To run USPEX correctly, there are some hints on the files in `Specific/` folder to control the structure relaxation in USPEX. We take example of VASP as an external code:

Your final structures have to be well relaxed, and energies — precise. The point is that your energy ranking has to be correct (to check this, look at

`E_series.pdf`file in the output).Your

`POTCAR`files: To yield correct results, the cores of your pseudopotentials (or PAW potentials) should not overlap by more than 10–15%.To have accurate relaxation at low cost, use the multistage relaxation with at least three stages of relaxation for each structure,

*i.e.*at least three`INCAR`files (`INCAR_1`,`INCAR_2`,`INCAR_3`, …). We usually set 4–5 stages of relaxation.Your initial structures will be usually very far from local minima, in such cases it helps to relax atoms and cell shape at constant volume first (

`ISIF`=4 in`INCAR_1,2`), then do full relaxation (`ISIF`=3 in`INCAR_3,4`), and finish with a very accurate single-point calculation (`ISIF`=2 and`NSW`=0 in`INCAR_5`).**Exceptions:**when you do fixed-cell predictions, and also in evolutionary metadynamics (except full relaxation) you must have`ISIF`=2.When your volume does not change, you can use default plane wave cutoff. When you use

`ISIF`=3, you must increase it by 30–40%, otherwise you get a large Pulay stress. Also your convergence criteria can be loose in the beginning, but have to be tight in the end:*e.g.*,`EDIFF`=1e-2 and`EDIFFG`=1e-1 in`INCAR_1`, gradually tightening to`EDIFF`=1e-4 and`EDIFFG`=1e-3 in`INCAR_4`. The maximum number of timesteps (`NSW`) should be sufficiently large to enable good relaxation, but not too large to avoid wasting computer time on poor configurations. The larger your system, the larger`NSW`should be.Choosing an efficient relaxation algorithm can save a lot of time. In VASP, we recommend to start relaxation with conjugate gradients (

`IBRION`=2 and`POTIM`=0.02) and when the structure is closer to local minimum, switch to`IBRION`=1 and`POTIM`=0.3.Even if you study an insulating system, many configurations that you will sample are going to be metallic, so to have well converged results, you must use “metallic” treatment — which works both for metals and insulators. We recommend the Methfessel-Paxton smearing scheme (

`ISMEAR`=1). For a clearly metallic system, use`ISMEAR`=1 and`SIGMA`=0.1–0.2. For a clearly insulating system, we recommend`ISMEAR`=1 and`SIGMA`starting at 0.1 (`INCAR_1`) and decreasing to 0.03–0.04.

Here we provide an example of `INCAR` files for carbon with 16 atoms in the unit cell, with default `ENCUT`=400 eV in `POTCAR`:

INCAR_1: PREC=LOW EDIFF=1e-2 EDIFFG=1e-1 NSW=65 ISIF=4 IBRION=2 POTIM=0.02 ISMEAR=1 SIGMA=0.10

INCAR_2: PREC=NORMAL EDIFF=1e-3 EDIFFG=1e-2 NSW=55 ISIF=4 IBRION=1 POTIM=0.30 ISMEAR=1 SIGMA=0.08

INCAR_3: PREC=NORMAL EDIFF=1e-3 EDIFFG=1e-2 ENCUT=520.0 NSW=65 ISIF=3 IBRION=2 POTIM=0.02 ISMEAR=1 SIGMA=0.07

INCAR_4: PREC=NORMAL EDIFF=1e-4 EDIFFG=1e-3 ENCUT=600.0 NSW=55 ISIF=3 IBRION=1 POTIM=0.30 ISMEAR=1 SIGMA=0.06

INCAR_5: PREC=NORMAL EDIFF=1e-4 EDIFFG=1e-3 ENCUT=600.0 NSW=0 ISIF=2 IBRION=2 POTIM=0.02 ISMEAR=1 SIGMA=0.05

The philosophy of METADYNAMICS is very similar to USPEX, except that we DO NOT change the cell shape during the META evolution. Therefore, we need to put `ISIF`=2 for all META steps. If the full relaxation mode is on, we can put `ISIF`=3 for the steps of full relaxation. Therefore, if we have the following set up:

% abinitioCode 1 1 1 (1 1) % ENDabinit

the `ISIF` should be “`2 2 2 3 3`” for `INCAR_1`, …, `INCAR_5` correspondingly.

Different from USPEX, VC-NEB method doesn’t need a structure relaxation from the external codes, which runs the structure relaxation in VC-NEB itself with the forces from external code calculation. Thus, there are some differences in the files. Take VASP `INCAR` files for example, we need to set `NSW`=0 to avoid the structure relaxation, but with `ISIF`=2 or 3 to extract the forces on the atoms, and the stress tensor on the lattice in VASP. We also suggest to use `PREC`=Accurate to have a good estimation for the forces and stress to accelerate the calculations for VC-NEB. An example of `INCAR` file for VC-NEB is presented below:

INCAR_1: PREC=Accurate EDIFF=1e-4 EDIFFG=1e-3 ENCUT=600.0 NSW=0 ISIF=2 IBRION=2 POTIM=0.02 ISMEAR=1 SIGMA=0.05