packmol: 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 CentOS possible default full paths are:

/usr/bin/packmol - from package: packmol

You may install the required package with command yum install {package}

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