Dear Lammps Users,

I am simulating Be system of particles whose lattice is described below(HCP). Z-dimension is kept in periodic. As a rule if any dimension is in periodicity, it should be defined in such a way that it should be in integral multiple of the lattice constant in that dimension.

Although I am using a multiple of **‘variable c’** (28 times of c in this case) but atoms are getting unstable at the boundaries.

Kindly suggest to make the periodicity work in Z-direction.

**variable a equal 2.312646565**

**variable b equal $a*sqrt(3.0)**

**variable c equal $a*1.5682**

**lattice custom 1.0 a1 $a 0.0 0.0&**

**a2 0.0 $b 0.0&**

**a3 0.0 0.0 $c&**

**basis 0.0 0.0 0.0&**

**basis 0.5 0.5 0.0&**

**basis 0.0 0.33333333 0.5&**

**basis 0.5 0.83333333 0.5**

**variable xi equal 0**

**variable xm equal 200**

**variable yi equal 0**

**variable ym equal 80**

**variable zi equal -50.77369281**

**variable zm equal 50.77369281**

**# Simulation box**

**region s_box block 0 350 0 200 (v_zi) (v_zm) units box**

The atoms are shown in Figure as below. they are loosing their structure at the boundaries.

**Regards.**