# Add Descriptor > Guides through adding a new descriptor type to deepmd-kit. Covers implementing in dpmodel (array-API-compatible), wrapping for JAX/pt_expt backends, hard-coding for PT/PD, registering arguments, and writing all required tests. - Skill: `deepmodeling/add-descriptor` (Agent Skill, multi-file: 3 files) - Install (CLI): `npx skillmds@latest add deepmodeling/add-descriptor` - Raw SKILL.md: https://api.skillmd.com/api/skills/deepmodeling/add-descriptor/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Integrations & APIs - License: LGPL-3.0-or-later - Author: deepmodeling (https://skillmd.com/u/deepmodeling) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/deepmodeling/add-descriptor --- # Adding a New Descriptor to deepmd-kit Follow these steps in order. Each step lists files to create/modify and patterns to follow. ## Step 1: Implement in dpmodel **Create** `deepmd/dpmodel/descriptor/.py` Inherit from `NativeOP` and `BaseDescriptor`. Register with decorators: ```python from deepmd.dpmodel import NativeOP from .base_descriptor import BaseDescriptor @BaseDescriptor.register("your_name") @BaseDescriptor.register("alias_name") # optional aliases class DescrptYourName(NativeOP, BaseDescriptor): ... ``` Key requirements: - `__init__`: initialize cutoff, sel, networks, davg/dstd statistics - `call(coord_ext, atype_ext, nlist, mapping=None)`: forward pass returning `(descriptor, rot_mat, g2, h2, sw)` - `serialize() -> dict`: save with `@class`, `type`, `@version`, `@variables` keys - `deserialize(cls, data)`: reconstruct from dict - Property/getter methods: `get_rcut`, `get_sel`, `get_dim_out`, `mixed_types`, etc. - `__getitem__`/`__setitem__` for `davg`/`dstd` access via multiple key aliases All dpmodel code **must** use `array_api_compat` for cross-backend compatibility (numpy/torch/jax/paddle). See [references/dpmodel-implementation.md](references/dpmodel-implementation.md) for full method table, array API pitfalls, and utilities. **Reference implementations**: - Simple: `deepmd/dpmodel/descriptor/se_e2_a.py` - Three-body: `deepmd/dpmodel/descriptor/se_t.py` - Attention-based: `deepmd/dpmodel/descriptor/dpa1.py` ## Step 2: Register **Edit** `deepmd/dpmodel/descriptor/__init__.py` — add import and `__all__` entry. **Edit** `deepmd/utils/argcheck.py` — register descriptor arguments: ```python @descrpt_args_plugin.register("your_name", alias=["alias"], doc="Description") def descrpt_your_name_args() -> list[Argument]: return [ Argument("sel", [list[int], str], optional=True, default="auto", doc=doc_sel), Argument("rcut", float, optional=True, default=6.0, doc=doc_rcut), Argument("rcut_smth", float, optional=True, default=0.5, doc=doc_rcut_smth), Argument( "neuron", list[int], optional=True, default=[10, 20, 40], doc=doc_neuron ), # ... add all constructor parameters ] ``` ## Step 3: Wrap for JAX backend **Create** `deepmd/jax/descriptor/.py` Pattern: `@flax_module` decorator + custom `__setattr__` for attribute conversion. ```python from deepmd.dpmodel.descriptor.your_name import DescrptYourName as DescrptYourNameDP from deepmd.jax.common import ArrayAPIVariable, flax_module, to_jax_array from deepmd.jax.descriptor.base_descriptor import BaseDescriptor from deepmd.jax.utils.exclude_mask import PairExcludeMask from deepmd.jax.utils.network import NetworkCollection @BaseDescriptor.register("your_name") @flax_module class DescrptYourName(DescrptYourNameDP): def __setattr__(self, name, value): if name in {"davg", "dstd"}: value = to_jax_array(value) if value is not None: value = ArrayAPIVariable(value) elif name in {"embeddings"}: if value is not None: value = NetworkCollection.deserialize(value.serialize()) elif name == "env_mat": pass # stateless elif name == "emask": value = PairExcludeMask(value.ntypes, value.exclude_types) return super().__setattr__(name, value) ``` For nested sub-components, define wrapper classes bottom-up. See `deepmd/jax/descriptor/dpa1.py` for example. **Edit** `deepmd/jax/descriptor/__init__.py` — add import and `__all__` entry. ## Step 4: Wrap for pt_expt backend **Create** `deepmd/pt_expt/descriptor/.py` The `@torch_module` decorator handles everything automatically: - Auto-generates `forward()` delegating to `call()` (and `forward_lower()` from `call_lower()`) - Auto-generates `__setattr__` that converts numpy arrays to torch buffers and dpmodel objects to pt_expt modules via a converter registry - Any unregistered `NativeOP` assigned as an attribute will raise `TypeError` — register it first Simple descriptors (no custom sub-components) need only an empty body: ```python from deepmd.dpmodel.descriptor.your_name import DescrptYourName as DescrptYourNameDP from deepmd.pt_expt.common import torch_module from deepmd.pt_expt.descriptor.base_descriptor import BaseDescriptor @BaseDescriptor.register("your_name") @torch_module class DescrptYourName(DescrptYourNameDP): pass ``` Standard dpmodel sub-components (`NetworkCollection`, `EmbeddingNet`, `PairExcludeMask`, `EnvMat`, `TypeEmbedNet`) are pre-registered in `deepmd/pt_expt/utils/` and converted automatically. No `__setattr__` override needed. For **custom sub-components** (e.g., a new block class inheriting `NativeOP`), create a separate wrapper file and register bottom-up with `register_dpmodel_mapping`: ```python # deepmd/pt_expt/descriptor/your_block.py from deepmd.dpmodel.descriptor.your_block import YourBlock as YourBlockDP from deepmd.pt_expt.common import register_dpmodel_mapping, torch_module @torch_module class YourBlock(YourBlockDP): pass register_dpmodel_mapping( YourBlockDP, lambda v: YourBlock.deserialize(v.serialize()), ) ``` Then import this module in `deepmd/pt_expt/descriptor/__init__.py` for its side effect (the registration must happen before the parent descriptor is instantiated). Reference: `deepmd/pt_expt/descriptor/se_t_tebd.py` + `se_t_tebd_block.py` **Edit** `deepmd/pt_expt/descriptor/__init__.py` — add import and `__all__` entry. ## Step 5: Hard-code for PT backend (if needed) **Create** `deepmd/pt/model/descriptor/.py` PT descriptors are fully reimplemented in PyTorch (not wrapping dpmodel). They inherit from `BaseDescriptor` and `torch.nn.Module`. Must implement `forward()`, `serialize()`, `deserialize()`. **Edit** `deepmd/pt/model/descriptor/__init__.py` — add import. Reference: `deepmd/pt/model/descriptor/se_a.py` ## Step 6: Hard-code for TF backend (if needed) **Create** `deepmd/tf/descriptor/.py` TF descriptors are fully reimplemented in TensorFlow. They inherit from `BaseDescriptor` and implement the TF computation graph. **Edit** `deepmd/tf/descriptor/__init__.py` — add import. Reference: `deepmd/tf/descriptor/se_a.py` ## Step 7: Hard-code for PD backend (if needed) Same as PT but using Paddle. Inherit from `BaseDescriptor` and `paddle.nn.Layer`. **Edit** `deepmd/pd/model/descriptor/__init__.py` — add import. Reference: `deepmd/pd/model/descriptor/se_a.py` ## Step 8: Write tests Eight test categories. See [references/test-patterns.md](references/test-patterns.md) for full code templates. pt_expt tests use `pytest.mark.parametrize` (not `itertools.product`), do not inherit from `unittest.TestCase`, and use `setup_method` (not `setUp`). | Test | File | Purpose | | --------------------- | -------------------------------------------------------------- | ------------------------------------------------- | | 8a. dpmodel | `source/tests/common/dpmodel/test_descriptor_.py` | Serialize/deserialize round-trip | | 8b. pt_expt | `source/tests/pt_expt/descriptor/test_.py` | Consistency + exportable + make_fx (float64 only) | | 8c. PT | `source/tests/pt/model/test_descriptor_.py` | PT hard-coded tests (if applicable) | | 8d. PD | `source/tests/pd/model/test_descriptor_.py` | PD hard-coded tests (if applicable) | | 8e. array_api_strict | `source/tests/array_api_strict/descriptor/.py` | Wrapper for consistency tests | | 8f. Universal dpmodel | `source/tests/universal/dpmodel/descriptor/test_descriptor.py` | Add parametrized entry | | 8g. Universal PT | `source/tests/universal/pt/descriptor/test_descriptor.py` | Add parametrized entry | | 8h. Consistency | `source/tests/consistent/descriptor/test_.py` | Cross-backend + API consistency | ## Step 9: Write documentation **Create** `doc/model/.md` Each descriptor needs a documentation page in `doc/model/`. Use MyST Markdown format with Sphinx extensions. List supported backends using icon substitutions. Template: ````markdown # Descriptor `"your_name"` {{ pytorch_icon }} {{ dpmodel_icon }} :::{note} **Supported backends**: PyTorch {{ pytorch_icon }}, DP {{ dpmodel_icon }} ::: Brief description of what the descriptor is and its theoretical motivation. ## Theory Mathematical formulation using LaTeX: ```math \mathcal{D}^i = ... ``` ## Instructions Example JSON configuration: ```json "descriptor": { "type": "your_name", "sel": [46, 92], "rcut_smth": 0.50, "rcut": 6.00, "neuron": [10, 20, 40], "resnet_dt": false, "seed": 1 } ``` Explain key parameters and link to the argument schema using `{ref}` directives, e.g. `{ref}rcut `. ```` Available backend icons: `{{ tensorflow_icon }}`, `{{ pytorch_icon }}`, `{{ jax_icon }}`, `{{ paddle_icon }}`, `{{ dpmodel_icon }}`. Only list backends that actually support this descriptor. **Edit** `doc/model/index.rst` — add the new page to the `toctree`: ```rst .. toctree:: :maxdepth: 1 ... ``` **Reference docs**: `doc/model/train-se-e2-r.md` (simple), `doc/model/dpa2.md` (modern) ## Verification ```bash # dpmodel self-consistency python -m pytest source/tests/common/dpmodel/test_descriptor_.py -v # pt_expt unit tests python -m pytest source/tests/pt_expt/descriptor/test_.py -v # Cross-backend consistency python -m pytest source/tests/consistent/descriptor/test_.py -v # PT/PD unit tests (if hard-coded) python -m pytest source/tests/pt/model/test_descriptor_.py -v python -m pytest source/tests/pd/model/test_descriptor_.py -v # Quick smoke test python -c " from deepmd.dpmodel.descriptor import DescrptYourName d = DescrptYourName(rcut=6.0, rcut_smth=1.8, sel=[20, 20]) d2 = DescrptYourName.deserialize(d.serialize()) print('Round-trip OK:', d.get_dim_out() == d2.get_dim_out()) " ``` ## Files summary | Step | Action | File | | ---- | ------ | -------------------------------------------------------------- | | 1 | Create | `deepmd/dpmodel/descriptor/.py` | | 2 | Edit | `deepmd/dpmodel/descriptor/__init__.py` | | 2 | Edit | `deepmd/utils/argcheck.py` | | 3 | Create | `deepmd/jax/descriptor/.py` | | 3 | Edit | `deepmd/jax/descriptor/__init__.py` | | 4 | Create | `deepmd/pt_expt/descriptor/.py` | | 4 | Edit | `deepmd/pt_expt/descriptor/__init__.py` | | 5 | Create | `deepmd/pt/model/descriptor/.py` (if needed) | | 5 | Edit | `deepmd/pt/model/descriptor/__init__.py` (if needed) | | 6 | Create | `deepmd/tf/descriptor/.py` (if needed) | | 6 | Edit | `deepmd/tf/descriptor/__init__.py` (if needed) | | 7 | Create | `deepmd/pd/model/descriptor/.py` (if needed) | | 7 | Edit | `deepmd/pd/model/descriptor/__init__.py` (if needed) | | 8a | Create | `source/tests/common/dpmodel/test_descriptor_.py` | | 8b | Create | `source/tests/pt_expt/descriptor/test_.py` | | 8c | Create | `source/tests/pt/model/test_descriptor_.py` (if PT) | | 8d | Create | `source/tests/pd/model/test_descriptor_.py` (if PD) | | 8e | Create | `source/tests/array_api_strict/descriptor/.py` | | 8e | Edit | `source/tests/array_api_strict/descriptor/__init__.py` | | 8f | Edit | `source/tests/universal/dpmodel/descriptor/test_descriptor.py` | | 8g | Edit | `source/tests/universal/pt/descriptor/test_descriptor.py` | | 8h | Create | `source/tests/consistent/descriptor/test_.py` | | 9 | Create | `doc/model/.md` | | 9 | Edit | `doc/model/index.rst` |