Feat: Support specifying proportion of atoms to be perturbed in System (#716)

See title.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit


- **New Features**
- Introduced a new parameter for controlled atom perturbation in the
perturb function, enhancing flexibility.

- **Bug Fixes**
- Improved logic for selecting atoms to perturb, ensuring only a
specified proportion is affected.

- **Tests**
- Added a new test class to validate the perturbation functionality for
atomic systems, increasing test coverage and reliability.
- Introduced a structured representation of a Silicon Carbide crystal
for validation in tests.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: Chengqian-Zhang

dpdata/system.py

@@ -849,6 +849,7 @@ def perturb(
         cell_pert_fraction: float,
         atom_pert_distance: float,
         atom_pert_style: str = "normal",
+        atom_pert_prob: float = 1.0,
     ):
         """Perturb each frame in the system randomly.
         The cell will be deformed randomly, and atoms will be displaced by a random distance in random direction.
@@ -877,6 +878,8 @@ def perturb(
                     These points are treated as vector used by atoms to move.
                     Obviously, the max length of the distance atoms move is `atom_pert_distance`.
                 - `'const'`: The distance atoms move will be a constant `atom_pert_distance`.
+        atom_pert_prob : float
+            Determine the proportion of the total number of atoms in a frame that are perturbed.
 
         Returns
         -------
@@ -900,7 +903,15 @@ def perturb(
                 tmp_system.data["coords"][0] = np.matmul(
                     tmp_system.data["coords"][0], cell_perturb_matrix
                 )
-                for kk in range(len(tmp_system.data["coords"][0])):
+                pert_natoms = int(atom_pert_prob * len(tmp_system.data["coords"][0]))
+                pert_atom_id = sorted(
+                    np.random.choice(
+                        range(len(tmp_system.data["coords"][0])),
+                        pert_natoms,
+                        replace=False,
+                    ).tolist()
+                )
+                for kk in pert_atom_id:
                     atom_perturb_vector = get_atom_perturb_vector(
                         atom_pert_distance, atom_pert_style
                     )

tests/poscars/POSCAR.SiC.partpert

@@ -0,0 +1,16 @@
+C4 Si4 
+1.0
+4.0354487481064565e+00 1.1027270790560616e-17 2.5642993008475204e-17 
+2.0693526054669642e-01 4.1066892997402196e+00 -8.6715682899078028e-18 
+4.2891472979598610e-01 5.5796885749827474e-01 4.1100061517204542e+00 
+C Si 
+4 4 
+Cartesian
+ 0.03122504  0.15559669  2.1913045
+ 1.93908836 -0.08678864  0.06748919
+ 0.13114716  2.15827511  0.06333341
+ 2.36161952  1.42824405  2.58837618
+-0.03895165  0.12197669  0.05496244
+ 1.79528462  2.48830207 -0.55733221
+ 2.11363589  0.09280028  2.0301803
+ 0.19221505  2.16245144  2.07930701

tests/test_perturb.py

@@ -12,13 +12,17 @@ class NormalGenerator:
     def __init__(self):
         self.randn_generator = self.get_randn_generator()
         self.rand_generator = self.get_rand_generator()
+        self.choice_generator = self.get_choice_generator()
 
     def randn(self, number):
         return next(self.randn_generator)
 
     def rand(self, number):
         return next(self.rand_generator)
 
+    def choice(self, total_natoms, pert_natoms, replace):
+        return next(self.choice_generator)[:pert_natoms]
+
     @staticmethod
     def get_randn_generator():
         data = np.asarray(
@@ -44,18 +48,26 @@ def get_rand_generator():
             [0.23182233, 0.87106847, 0.68728511, 0.94180274, 0.92860453, 0.69191187]
         )
 
+    @staticmethod
+    def get_choice_generator():
+        yield np.asarray([5, 3, 7, 6, 2, 1, 4, 0])
+
 
 class UniformGenerator:
     def __init__(self):
         self.randn_generator = self.get_randn_generator()
         self.rand_generator = self.get_rand_generator()
+        self.choice_generator = self.get_choice_generator()
 
     def randn(self, number):
         return next(self.randn_generator)
 
     def rand(self, number):
         return next(self.rand_generator)
 
+    def choice(self, total_natoms, pert_natoms, replace):
+        return next(self.choice_generator)
+
     @staticmethod
     def get_randn_generator():
         data = [
@@ -97,18 +109,26 @@ def get_rand_generator():
             yield np.asarray(data[count])
             count += 1
 
+    @staticmethod
+    def get_choice_generator():
+        yield np.asarray([5, 3, 7, 6, 2, 1, 4, 0])
+
 
 class ConstGenerator:
     def __init__(self):
         self.randn_generator = self.get_randn_generator()
         self.rand_generator = self.get_rand_generator()
+        self.choice_generator = self.get_choice_generator()
 
     def randn(self, number):
         return next(self.randn_generator)
 
     def rand(self, number):
         return next(self.rand_generator)
 
+    def choice(self, total_natoms, pert_natoms, replace):
+        return next(self.choice_generator)
+
     @staticmethod
     def get_randn_generator():
         data = np.asarray(
@@ -135,13 +155,18 @@ def get_rand_generator():
             [0.01525907, 0.68387374, 0.39768541, 0.55596047, 0.26557088, 0.60883073]
         )
 
+    @staticmethod
+    def get_choice_generator():
+        yield np.asarray([5, 3, 7, 6, 2, 1, 4, 0])
+
 
 # %%
 class TestPerturbNormal(unittest.TestCase, CompSys, IsPBC):
     @patch("numpy.random")
     def setUp(self, random_mock):
         random_mock.rand = NormalGenerator().rand
         random_mock.randn = NormalGenerator().randn
+        random_mock.choice = NormalGenerator().choice
         system_1_origin = dpdata.System("poscars/POSCAR.SiC", fmt="vasp/poscar")
         self.system_1 = system_1_origin.perturb(1, 0.05, 0.6, "normal")
         self.system_2 = dpdata.System("poscars/POSCAR.SiC.normal", fmt="vasp/poscar")
@@ -153,6 +178,7 @@ class TestPerturbUniform(unittest.TestCase, CompSys, IsPBC):
     def setUp(self, random_mock):
         random_mock.rand = UniformGenerator().rand
         random_mock.randn = UniformGenerator().randn
+        random_mock.choice = UniformGenerator().choice
         system_1_origin = dpdata.System("poscars/POSCAR.SiC", fmt="vasp/poscar")
         self.system_1 = system_1_origin.perturb(1, 0.05, 0.6, "uniform")
         self.system_2 = dpdata.System("poscars/POSCAR.SiC.uniform", fmt="vasp/poscar")
@@ -164,11 +190,24 @@ class TestPerturbConst(unittest.TestCase, CompSys, IsPBC):
     def setUp(self, random_mock):
         random_mock.rand = ConstGenerator().rand
         random_mock.randn = ConstGenerator().randn
+        random_mock.choice = ConstGenerator().choice
         system_1_origin = dpdata.System("poscars/POSCAR.SiC", fmt="vasp/poscar")
         self.system_1 = system_1_origin.perturb(1, 0.05, 0.6, "const")
         self.system_2 = dpdata.System("poscars/POSCAR.SiC.const", fmt="vasp/poscar")
         self.places = 6
 
 
+class TestPerturbPartAtoms(unittest.TestCase, CompSys, IsPBC):
+    @patch("numpy.random")
+    def setUp(self, random_mock):
+        random_mock.rand = NormalGenerator().rand
+        random_mock.randn = NormalGenerator().randn
+        random_mock.choice = NormalGenerator().choice
+        system_1_origin = dpdata.System("poscars/POSCAR.SiC", fmt="vasp/poscar")
+        self.system_1 = system_1_origin.perturb(1, 0.05, 0.6, "normal", 0.25)
+        self.system_2 = dpdata.System("poscars/POSCAR.SiC.partpert", fmt="vasp/poscar")
+        self.places = 6
+
+
 if __name__ == "__main__":
     unittest.main()