class_docstr: Entry for Density Matrix (DM)
  The density matrix is used to express total energy of both non-interacting and
  interacting systems.
  
  Notes
  -----
  dm entry can only have 1 system
class_docstr_tok: ["Entry","for","Density","Matrix","(","DM",")","The","density","matrix","is","used","to","express","total","energy","of","both","non-interacting","and","interacting","systems",".","Notes","--","--","-","dm","entry","can","only","have","1","system"]
code: def entry_type(self) -> str:
      return "dm"
  
imports: from __future__ import annotations
  from abc import abstractmethod, abstractproperty
  from typing import List, Dict, Optional
  import numpy
  from dqc.system.mol import Mol
  from dqc.system.base_system import BaseSystem
  from deepchem.utils.dftutils import KSCalc
  from deepchem.utils.dft_utils import parse_moldesc, BaseGrid
label_desc: Use image node_id 2 for calling the _EntryDM obj's underlying member method code with example usage: obj.entry_type() and returns: str