ASE on your local PC

2025 June 16, updated

ASE provides interfaces to different codes. ASE also includes Pure Python EMT calculator, which is suitable for testing CrySPY because of its fast and easy structure optimization.

In this tutorial, we try to use CrySPY in your local PC (Mac or Linux). The target system is Cu 8 atoms.

Assumption

Here, we assume the following conditions:

  • CrySPY 1.2.0 or later in your local PC
  • CrySPY job filename: job_cryspy
  • ase input filename: ase_in.py

Input files

Move to your working directory, and copy the example files by one of the following methods.

cd ase_Cu8_RS
tree

.
├── calc_in
│   ├── ase_in.py_1
│   └── job_cryspy
└── cryspy.in

cryspy.in

cryspy.in is the input file of CrySPY.

[basic]
algo = RS
calc_code = ASE
tot_struc = 5
nstage = 1
njob = 5
jobcmd = zsh
jobfile = job_cryspy

[structure]
atype = Cu
nat = 8

[ASE]
ase_python = ase_in.py

[option]

In [basic] section, jobcmd = zsh can be changed to jobcmd = sh or jobcmd = bash in accordance with your environment. CrySPY runs zsh job_cryspy as a background job internally.

[ASE] section is required when you use ASE.

You can name the following files whatever you want:

  • jobfile: job_cryspy
  • ase_python: ase_in.py

The other input variables are discussed later.

calc_in directory

The job file and input files for ASE are prepared in this directory.

Job file

The name of the job file must match the value of jobfile in cryspy.in. The example of job file (here, job_cryspy) is shown below.

#!/bin/sh

# ---------- ASE
python3 ase_in.py

# ---------- CrySPY
sed -i -e '3 s/^.*$/done/' stat_job

You can specify the input (ase_in.py) file names, but it must match the values of ase_python in cryspy.in. You must add sed -i -e '3 s/^.*$/done/' stat_job at the end of the file in CrySPY.

Note

sed -i -e '3 s/^.*$/done/' stat_job is required at the end of the job file.

Tip

In the job file of CrySPY, the string CrySPY_ID is automatically replaced with the structure ID. When you use a job scheduler such as PBS and SLURM, it is useful to set the structure ID to the job name. For example, in the PBS system, #PBS -N Si_CrySPY_ID in ID 10 is replaced with #PBS -N Si_10. Note that starting with a number will result in an error. You should add a prefix like Si_.

Input for ASE

Input files based on the number of stages (nstage in cryspy.in) are required. Name the input file(s) with a suffix _x. Here x means the stage number.

We are using nstage = 1 in this ASE tutorial, so we need only ase_in.py_1. ase_in.py_1 is listed below. Refer to the ASE documentation for details.

from ase.constraints import FixSymmetry
from ase.filters import FrechetCellFilter
from ase.calculators.emt import EMT
from ase.optimize import BFGS
import numpy as np
from ase.io import read, write

# ---------- input structure
# CrySPY outputs 'POSCAR' as an input file in work/xxxxxx directory
atoms = read('POSCAR', format='vasp')

# ---------- setting and run
atoms.calc = EMT()
atoms.set_constraint([FixSymmetry(atoms)])
cell_filter = FrechetCellFilter(atoms, hydrostatic_strain=False)
opt = BFGS(cell_filter)
opt.run(fmax=0.01, steps=2000)

# ---------- opt. structure and energy
# [rule in ASE interface]
# output file for energy: 'log.tote' in eV/cell
#                         CrySPY reads the last line of 'log.tote'
# output file for structure: 'CONTCAR' in vasp format
e = cell_filter.atoms.get_total_energy()
with open('log.tote', mode='w') as f:
    f.write(str(e))

# ------ write structure
opt_atoms = cell_filter.atoms.copy()
opt_atoms.set_constraint(None)    # remove constraint for pymatgen
write('CONTCAR', opt_atoms, format='vasp', direct=True)

Unlike VASP and QE, the ASE input (python script) is more flexible. CrySPY has two rules:

  1. Energy is output in units of eV/cell to log.tote file. CrySPY reads the last line of it.
  2. Optimized structure is output to CONTCAR file in the VASP format.

Running CrySPY

Go to Running CrySPY