Hello Steve

I am trying to find surface energy of triclinic cell of Al using the energy minimization techniques.

My input file goes as

## 3d Al simulation

# Atom definition

variable lat equal 4.05

variable skin equal 0.3

variable cutoff equal {lat}/sqrt(2.0)+{skin}

variable T_initial equal 2

variable T_final equal 2

variable steps equal 50000

units metal

boundary p p s

atom_style atomic

lattice fcc 4.05

region box prism 0 10 0 10 0 10 0 0 0

create_box 1 box

create_atoms 1 box

pair_style eam

pair_coeff * * Al_jnp.eam

neighbor ${skin} bin

neigh_modify delay 5

region lower block INF INF INF INF INF 0.25

region upper block INF INF INF INF 5.75 INF

group lower region lower

group upper region upper

group boundary union lower upper

group mobile subtract all boundary

######### Thermo output (Loop Start) ############

fix 1 lower setforce 0.0 0.0 0.0

thermo 10

thermo_style custom step cpu etotal ke lx ly lz pxx pyy pzz pxy pyz pxz temp press #c_vir_ken

thermo_modify line one format float %11.7g

variable loop1 equal 5

variable n_strain loop {loop1}
variable lambda equal 1+0.001*{n_strain}

displace_box all x scale {lambda} y scale {lambda} xy final 1.005

print “”

print “**"**”

print “with strain: n_strain = {n_strain}, lambda = {lambda}”

print "

print “”

minimize 1.0e-9 1.0e-8 1000 10000

next n_strain

jump in.Surf22

############# LOOP END ##################

The strain is applied in (11), (22) and (12) direction wile keeping the prism non periodic in Z. I want to plot Total energy as a function of thickness. It should be a linear curve and the intercept will give me a value for surface energy. My problem is when I run the minimization I get a negative value of Surface energy, while I expect the value to be positive.

Can you look at the input script and point out any potential errors (if any).

Regards