dl_poly_openmpi: 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/lib64/openmpi/bin/dl_poly_openmpi - from package: dl_poly-openmpi

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

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