added two examples which existed in the main i-pi repo but not here.

examples/lammps/graphene/C.opt.tersoff

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+# Tersoff parameters for various elements and mixtures
+# multiple entries can be added to this file, LAMMPS reads the ones it needs
+# these entries are in LAMMPS "metal" units:
+#   A,B = eV; lambda1,lambda2,lambda3 = 1/Angstroms; R,D = Angstroms
+#   other quantities are unitless
+
+# Aidan Thompson (athomps at sandia.gov) takes full blame for this
+# file.  It specifies various potentials published by J. Tersoff for
+# silicon, carbon and germanium. Since Tersoff published several
+# different silicon potentials, I refer to them using atom types
+# Si(B), Si(C) and Si(D). The last two are almost almost identical but
+# refer to two different publications. These names should be used in
+# the LAMMPS command when the file is invoked. For example:
+# pair_coeff * * SiCGe.tersoff Si(B).  The Si(D), C and Ge potentials
+# can be used pure silicon, pure carbon, pure germanium, binary SiC,
+# and binary SiGe, but not binary GeC or ternary SiGeC. LAMMPS will
+# generate an error if this file is used with any combination
+# involving C and Ge, since there are no entries for the GeC
+# interactions (Tersoff did not publish parameters for this
+# cross-interaction.)
+
+# format of a single entry (one or more lines):
+#   element 1, element 2, element 3, 
+#   m, gamma, lambda3, c, d, costheta0, n, beta, lambda2, B, R, D, lambda1, A
+
+# The original Tersoff potential for Silicon, Si(B)
+# J. Tersoff, PRB, 37, 6991 (1988) 
+
+Si(B)  Si(B)   Si(B)  3.0 1.0 1.3258 4.8381 2.0417 0.0000 22.956
+             0.33675  1.3258  95.373  3.0  0.2  3.2394  3264.7
+
+# The later Tersoff potential for Silicon, Si(C)
+# J. Tersoff, PRB, 38, 9902 (1988) 
+
+Si(C)  Si(C)   Si(C)  3.0 1.0 1.7322 1.0039e5 16.218 -0.59826 0.78734
+             1.0999e-6  1.7322  471.18  2.85  0.15  2.4799  1830.8
+
+# The later Tersoff potential for Carbon, Silicon, and Germanium
+# J. Tersoff, PRB, 39, 5566 (1989) + errata (PRB 41, 3248)
+# The Si and C parameters are very close to those in SiC.tersoff
+
+C      C       C         3.0 1.0 0.0 3.8049e4 4.3484 -0.57058 0.72751 1.5724e-7  2.2119  346.74    1.95    0.15   3.4879  1393.6
+Si(D)  Si(D)   Si(D)     3.0 1.0 0.0 1.0039e5 16.217 -0.59825 0.78734 1.1000e-6  1.7322  471.18    2.85    0.15   2.4799  1830.8
+Ge     Ge      Ge        3.0 1.0 0.0 1.0643e5 15.652 -0.43884 0.75627 9.0166e-7  1.7047  419.23    2.95    0.15   2.4451  1769.0
+
+C      Si(D)   Si(D)     3.0 1.0 0.0 3.8049e4 4.3484 -0.57058 0.72751 1.5724e-7  1.97205 395.1451  2.3573  0.1527 2.9839  1597.3111
+C      Si(D)   C         3.0 1.0 0.0 3.8049e4 4.3484 -0.57058 0.72751 0.0        0.0     0.0       1.95    0.15   0.0     0.0
+C      C       Si(D)     3.0 1.0 0.0 3.8049e4 4.3484 -0.57058 0.72751 0.0        0.0     0.0       2.3573  0.1527 0.0     0.0
+
+Si(D)  C       C         3.0 1.0 0.0 1.0039e5 16.217 -0.59825 0.78734 1.1000e-6  1.97205 395.1451  2.3573  0.1527 2.9839  1597.3111
+Si(D)  Si(D)   C         3.0 1.0 0.0 1.0039e5 16.217 -0.59825 0.78734 0.0        0.0     0.0       2.3573  0.1527 0.0     0.0
+Si(D)  C       Si(D)     3.0 1.0 0.0 1.0039e5 16.217 -0.59825 0.78734 0.0        0.0     0.0       2.85    0.15   0.0     0.0
+
+Si(D)  Ge      Ge        3.0 1.0 0.0 1.0039e5 16.217 -0.59825 0.78734 1.1000e-6  1.71845 444.7177  2.8996  0.1500 2.4625  1799.6347
+Si(D)  Si(D)   Ge        3.0 1.0 0.0 1.0039e5 16.217 -0.59825 0.78734 0.0        0.0     0.0       2.8996  0.1500 0.0     0.0
+Si(D)  Ge      Si(D)     3.0 1.0 0.0 1.0039e5 16.217 -0.59825 0.78734 0.0        0.0     0.0       2.85    0.15   0.0     0.0
+
+Ge     Si(D)   Si(D)     3.0 1.0 0.0 1.0643e5 15.652 -0.43884 0.75627 9.0166e-7  1.71845 444.7177  2.8996  0.1500 2.4625  1799.6347
+Ge     Si(D)   Ge        3.0 1.0 0.0 1.0643e5 15.652 -0.43884 0.75627 0.0        0.0     0.0       2.95    0.15   0.0     0.0
+Ge     Ge      Si(D)     3.0 1.0 0.0 1.0643e5 15.652 -0.43884 0.75627 0.0        0.0     0.0       2.8996  0.1500 0.0     0.0
+
+# Optimized Tersoff for Carbon: Lindsay and Broido PRB 81, 205441 (2010) 
+#   element 1, element 2, element 3, 
+#   m, gamma, lambda3, c, d, costheta0, n, beta, lambda2, B, R, D, lambda1, A
+C(O)    C(O)   C(O)     3.0 1.0 0.0 3.8049e4 4.3484 -0.930 0.72751 1.5724e-7  2.2119  430.0    1.95    0.15   3.4879  1393.6
+

examples/lammps/graphene/in.lmp

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+atom_style	atomic
+units   	metal
+dimension	3
+boundary 	p p p
+processors      * * 1
+
+read_data       ./data.lmp
+mass		1 12.01  ##Carbon
+
+### Optimized Tersoff for Carbon: Lindsay and Broido PRB 81, 205441 (2010) 
+pair_style      tersoff
+pair_coeff      * * C.opt.tersoff C(O) 
+
+variable	T equal 300
+variable        V equal vol
+
+variable        Lx equal xhi-xlo
+variable        Ly equal yhi-ylo
+print           "Lx = ${Lx} A"
+print           "Ly = ${Ly} A"
+
+print           "Volume simulation box = $V A^(3)"
+variable        Volume equal v_Lx*v_Ly*3.35
+print           "Volume = Lx*Ly*3.35A = ${Volume} A^(3)"
+
+velocity	all create $T 345352 mom yes rot yes dist gaussian
+timestep  	0.001  # 0.001 picosecond = 1 femtosecond
+thermo          1000
+thermo_style    custom step temp pe etotal press pxx pyy pzz
+
+fix		1  all ipi graphene 31415 unix
+run		5000000
+