lammps: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/lammps - from package: lammps

You may install the required package with command apt-get install {package}

Error in other languages:
lammps: bevel nie gevind nie
lammps: comandă negăsită
lammps: comando não encontrado
lammps: commande introuvable
lammps: command not found
lammps: käsku ei ole
lammps: không tìm thấy lệnh
lammps: komanda nerasta
lammps: Kommando nicht gefunden.
lammps: kommandot finns inte
lammps: komut yok
lammps: nie znaleziono polecenia
lammps: níor aimsíodh an t-ordú
lammps: no se encontró la orden
lammps: no s'ha trobat l'ordre
lammps: opdracht niet gevonden
lammps: parancs nem található
lammps: perintah tidak ditemukan
lammps: príkaz nenájdený
lammps: příkaz nenalezen
lammps: команда не найдена
lammps: командата не е открита
lammps: 命令找不到
lammps: コマンドが見つかりません