feat: add pair table model to pytorch

deepmd/pt/model/model/pair_tab.py

@@ -0,0 +1,351 @@
+from .atomic_model import AtomicModel
+from deepmd.utils.pair_tab import (
+    PairTab,
+)
+import logging
+import torch
+from torch import nn
+import numpy as np
+from typing import Dict, List, Optional, Union
+
+from deepmd.model_format import FittingOutputDef, OutputVariableDef
+
+class PairTabModel(nn.Module, AtomicModel):
+    """Pairwise tabulation energy model.
+
+    This model can be used to tabulate the pairwise energy between atoms for either
+    short-range or long-range interactions, such as D3, LJ, ZBL, etc. It should not
+    be used alone, but rather as one submodel of a linear (sum) model, such as
+    DP+D3.
+
+    Do not put the model on the first model of a linear model, since the linear
+    model fetches the type map from the first model.
+
+    At this moment, the model does not smooth the energy at the cutoff radius, so
+    one needs to make sure the energy has been smoothed to zero.
+
+    Parameters
+    ----------
+    tab_file : str
+        The path to the tabulation file.
+    rcut : float
+        The cutoff radius.
+    sel : int or list[int]
+        The maxmum number of atoms in the cut-off radius.
+    """
+
+    def __init__(
+        self, tab_file: str, rcut: float, sel: Union[int, List[int]], **kwargs
+    ):
+        super().__init__() 
+        self.tab_file = tab_file
+        self.rcut = rcut
+
+        # check table data against rcut and update tab_file if needed.
+        self._check_table_upper_boundary()
+
+        self.tab = PairTab(self.tab_file)
+        self.ntypes = self.tab.ntypes
+
+
+        tab_info, tab_data = self.tab.get() # this returns -> Tuple[np.array, np.array]
+        self.tab_info = torch.from_numpy(tab_info) 
+        self.tab_data = torch.from_numpy(tab_data)
+
+        # self.model_type = "ener"
+        # self.model_version = MODEL_VERSION ## this shoud be in the parent class
+
+        if isinstance(sel, int):
+            self.sel = sel
+        elif isinstance(sel, list):
+            self.sel = sum(sel)
+        else:
+            raise TypeError("sel must be int or list[int]")
+
+    def get_fitting_output_def(self)->FittingOutputDef:
+        return FittingOutputDef(
+            [OutputVariableDef(
+                name="energy",
+                shape=[1],
+                reduciable=True,
+                differentiable=True
+            )]
+        )
+
+    def get_rcut(self)->float:
+        return self.rcut
+
+    def get_sel(self)->int:
+        return self.sel
+
+    def distinguish_types(self)->bool:
+        # to match DPA1 and DPA2.
+        return False
+
+    def forward_atomic(
+        self,
+        extended_coord, 
+        extended_atype, 
+        nlist,
+        mapping: Optional[torch.Tensor] = None,
+        do_atomic_virial: bool = False,
+        ) -> Dict[str, torch.Tensor]:
+
+
+        nframes, nloc, nnei = nlist.shape
+
+        #this will mask all -1 in the nlist
+        masked_nlist = torch.clamp(nlist,0)
+
+        atype = extended_atype[:, :nloc] #(nframes, nloc)
+        pairwise_dr = self._get_pairwise_dist(extended_coord) # (nframes, nall, nall, 3)
+        pairwise_rr = pairwise_dr.pow(2).sum(-1).sqrt() # (nframes, nall, nall)
+
+        self.tab_data = self.tab_data.reshape(self.tab.ntypes,self.tab.ntypes,self.tab.nspline,4)
+
+        #to calculate the atomic_energy, we need 3 tensors, i_type, j_type, rr
+        #i_type : (nframes, nloc), this is atype.
+        #j_type : (nframes, nloc, nnei)
+        j_type = extended_atype[torch.arange(extended_atype.size(0))[:, None, None], masked_nlist]
+
+        #slice rr to get (nframes, nloc, nnei)
+        rr = torch.gather(pairwise_rr[:, :nloc, :],2, masked_nlist)
+
+        raw_atomic_energy = self._pair_tabulated_inter(atype, j_type, rr)
+
+        atomic_energy = 0.5 * torch.sum(torch.where(nlist != -1, raw_atomic_energy, torch.zeros_like(raw_atomic_energy)) ,dim=-1)
+
+        return {"energy": atomic_energy}
+
+    def _check_table_upper_boundary(self):
+        """Update User Provided Table Based on `rcut`
+
+        This function checks the upper boundary provided in the table against rcut.
+        If the table upper boundary values decay to zero before rcut, padding zeros will
+        be add to the table to cover rcut; if the table upper boundary values do not decay to zero
+        before ruct, linear extrapolation will be performed to rcut. In both cases, the table file
+        will be overwritten.
+
+        Example
+        -------
+
+        table = [[0.005 1.    2.    3.   ]
+                [0.01  0.8   1.6   2.4  ]
+                [0.015 0.    1.    1.5  ]]
+
+        rcut = 0.022
+
+        new_table = [[0.005 1.    2.    3.   ]
+                    [0.01  0.8   1.6   2.4  ]
+                    [0.015 0.    1.    1.5  ]
+                    [0.02  0.    0.5   0.75 ]
+                    [0.025 0.    0.    0.   ]]
+
+        ----------------------------------------------
+
+        table = [[0.005 1.    2.    3.   ]
+                [0.01  0.8   1.6   2.4  ]
+                [0.015 0.5   1.    1.5  ]
+                [0.02  0.25  0.4   0.75 ]
+                [0.025 0.    0.1   0.   ]
+                [0.03  0.    0.    0.   ]] 
+
+        rcut = 0.031    
+
+        new_table = [[0.005 1.    2.    3.   ]
+                    [0.01  0.8   1.6   2.4  ]
+                    [0.015 0.5   1.    1.5  ]
+                    [0.02  0.25  0.4   0.75 ]
+                    [0.025 0.    0.1   0.   ]
+                    [0.03  0.    0.    0.   ]
+                    [0.035 0.    0.    0.   ]]       
+        """
+
+        raw_data = np.loadtxt(self.tab_file)
+        upper = raw_data[-1][0]
+        upper_val = raw_data[-1][1:]
+        upper_idx  = raw_data.shape[0] - 1
+        increment = raw_data[1][0] - raw_data[0][0]
+
+        #the index of table for the grid point right after rcut
+        rcut_idx = int(self.rcut/increment)
+
+        if np.all(upper_val == 0):
+            # if table values decay to `0` after rcut
+            if self.rcut < upper and np.any(raw_data[rcut_idx-1][1:]!=0):
+                logging.warning(
+                    "The energy provided in the table does not decay to 0 at rcut."
+                )
+            # if table values decay to `0` at rcut, do nothing
+
+            # if table values decay to `0` before rcut, pad table with `0`s.
+            elif self.rcut > upper:
+                pad_zero = np.zeros((rcut_idx - upper_idx,4))
+                pad_zero[:,0] = np.linspace(upper + increment, increment*(rcut_idx+1), rcut_idx-upper_idx)
+                raw_data = np.concatenate((raw_data,pad_zero),axis=0)
+        else:
+            # if table values do not decay to `0` at rcut
+            if self.rcut <= upper:
+                logging.warning(
+                    "The energy provided in the table does not decay to 0 at rcut."
+                )
+            # if rcut goes beyond table upper bond, need extrapolation.
+            else:
+                logging.warning(
+                    "The rcut goes beyond table upper boundary, performing linear extrapolation."
+                )
+                pad_linear = np.zeros((rcut_idx - upper_idx+1,4))
+                pad_linear[:,0] = np.linspace(upper, increment*(rcut_idx+1), rcut_idx-upper_idx+1)
+                pad_linear[:,1:] = np.array([
+                    np.linspace(start, 0, rcut_idx - upper_idx+1) for start in upper_val
+                ]).T
+                raw_data = np.concatenate((raw_data[:-1,:],pad_zero),axis=0)
+
+        #over writing file with padding if applicable.
+        with open(self.tab_file, 'wb') as f:
+            np.savetxt(f, raw_data)
+
+    def _pair_tabulated_inter(self, nlist: torch.Tensor,i_type: torch.Tensor, j_type: torch.Tensor, rr: torch.Tensor) -> torch.Tensor:
+        """Pairwise tabulated energy.
+        
+        Parameters
+        ----------
+        nlist : torch.Tensor
+            The unmasked neighbour list. (nframes, nloc)
+
+        i_type : torch.Tensor
+            The integer representation of atom type for all local atoms for all frames. (nframes, nloc)
+
+        j_type : torch.Tensor
+            The integer representation of atom type for all neighbour atoms of all local atoms for all frames. (nframes, nloc, nnei)
+
+        rr : torch.Tensor
+            The salar distance vector between two atoms. (nframes, nloc, nnei)
+        
+        Returns
+        -------
+        torch.Tensor
+            The masked atomic energy for all local atoms for all frames. (nframes, nloc, nnei)
+        
+        Raises
+        ------
+        Exception
+            If the distance is beyond the table.
+        
+        Notes
+        -----
+        This function is used to calculate the pairwise energy between two atoms.
+        It uses a table containing cubic spline coefficients calculated in PairTab.
+        """
+
+        rmin = self.tab_info[0] 
+        hh = self.tab_info[1]
+        hi = 1. / hh
+
+        self.nspline = int(self.tab_info[2] + 0.1)
+
+        uu = (rr - rmin) * hi # this is broadcasted to (nframes,nloc,nnei)
+
+
+        # if nnei of atom 0 has -1 in the nlist, uu would be 0.
+        # this is to handel the nlist where the mask is set to 0.
+        # by replacing the values wiht nspline + 1, the energy contribution will be 0
+        uu = torch.where(nlist != -1, uu, self.nspline+1)
+
+        if torch.any(uu < 0):
+            raise Exception("coord go beyond table lower boundary")
+
+        idx = uu.to(torch.int)
+
+        uu -= idx
+
+
+        final_coef = self._extract_spline_coefficient(i_type, j_type, idx)
+
+        a3, a2, a1, a0 = torch.unbind(final_coef, dim=-1) # 4 * (nframes, nloc, nnei)
+
+        etmp = (a3 * uu + a2) * uu + a1 # this should be elementwise operations.
+        ener = etmp * uu + a0
+        return ener
+
+    @staticmethod
+    def _get_pairwise_dist(coords: torch.Tensor) -> torch.Tensor:
+        """Get pairwise distance `dr`.
+
+        Parameters
+        ----------
+        coords : torch.Tensor
+            The coordinate of the atoms shape of (nframes * nall * 3).
+
+        Returns
+        -------
+        torch.Tensor
+            The pairwise distance between the atoms (nframes * nall * nall * 3).
+        
+        Examples
+        --------
+        coords = torch.tensor([[
+                [0,0,0],
+                [1,3,5],
+                [2,4,6]
+            ]])
+        
+        dist = tensor([[
+            [[ 0,  0,  0],
+            [-1, -3, -5],
+            [-2, -4, -6]],
+
+            [[ 1,  3,  5],
+            [ 0,  0,  0],
+            [-1, -1, -1]],
+
+            [[ 2,  4,  6],
+            [ 1,  1,  1],
+            [ 0,  0,  0]]
+            ]])
+        """
+        return coords.unsqueeze(2) - coords.unsqueeze(1)
+
+    def _extract_spline_coefficient(self, i_type: torch.Tensor, j_type: torch.Tensor, idx: torch.Tensor) -> torch.Tensor:
+        """Extract the spline coefficient from the table.
+
+        Parameters
+        ----------
+        i_type : torch.Tensor
+            The integer representation of atom type for all local atoms for all frames. (nframes, nloc)
+
+        j_type : torch.Tensor
+            The integer representation of atom type for all neighbour atoms of all local atoms for all frames. (nframes, nloc, nnei)
+
+        idx : torch.Tensor
+            The index of the spline coefficient. (nframes, nloc, nnei)
+
+        Returns
+        -------
+        torch.Tensor
+            The spline coefficient. (nframes, nloc, nnei, 4)
+
+        Example
+        -------
+
+        """
+
+        # (nframes, nloc, nnei)
+        expanded_i_type = i_type.unsqueeze(-1).expand(-1, -1, j_type.shape[-1])
+
+        # (nframes, nloc, nnei, nspline, 4)
+        expanded_tab_data = self.tab_data[expanded_i_type, j_type]
+
+        # (nframes, nloc, nnei, 1, 4)
+        expanded_idx = idx.unsqueeze(-1).unsqueeze(-1).expand(-1, -1,-1, -1, 4)
+
+        #handle the case where idx is beyond the number of splines
+        clipped_indices = torch.clamp(expanded_idx, 0, self.nspline - 1).to(torch.int64)
+
+        # (nframes, nloc, nnei, 4)
+        final_coef = torch.gather(expanded_tab_data, 3, clipped_indices).squeeze()
+
+        # when the spline idx is beyond the table, all spline coefficients are set to `0`, and the resulting ener corresponding to the idx is also `0`.
+        final_coef[expanded_idx.squeeze() >= self.nspline] = 0
+
+        return final_coef