<Brenner_params n_types="1" label="Brenner1">
  <!-- First set of parameters from Brenner(1990) -->
  <per_type_data type="1" atomic_num="6" />
  <per_pair_data atnum_i="6" atnum_j="6" R1="1.7" R2="2.0" De="6.325" S="1.29"
     beta="1.5" delta="0.80469" Re="1.315" shift="0.0" />
  <per_triplet_data atnum_c="6" atnum_j="6" atnum_k="6"
     a0="0.011304" c0="19.0" d0="2.5" />
</Brenner_params>

<Brenner_params n_types="1" label="Brenner2">
  <!-- Second set of parameters from Brenner(1990) -->
  <per_type_data type="1" atomic_num="6" />
  <per_pair_data atnum_i="6" atnum_j="6" R1="1.7" R2="2.0" De="6.0" S="1.22"
     beta="2.1" delta="0.5" Re="1.390" shift="0.0" />
  <per_triplet_data atnum_c="6" atnum_j="6" atnum_k="6"
     a0="0.00020813" c0="330.0" d0="3.5" />
</Brenner_params>

<Brenner_params n_types="1" label="graphene">
 <!-- 2nd set of parameters from Brenner (1990), with Re scaled to
  give graphene lattice constant of 1.42 A and delta and shift modified
  to match ab initio graphene elastic constants, as described in Arroyo
  et al, Phys. Rev. B. 69 115415 (2004).
  Gives Poission ratio 0.149, Youngs modulus in plane 342 J/m^2 and
  bending modulus 3.9 eV A^2 per atom, in very good agreement with
  Kudin et al, Phys. Rev. B. 64 235406 (2001) -->

  <per_type_data type="1" atomic_num="6" />
  <per_pair_data atnum_i="6" atnum_j="6" R1="1.7" R2="2.0" De="6.0" S="1.22"
     beta="2.1" delta="0.95" Re="1.360" shift="0.03" />
  <per_triplet_data atnum_c="6" atnum_j="6" atnum_k="6"
     a0="0.00020813" c0="330.0" d0="3.5" />
</Brenner_params>