dl_poly_mpich: 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/mpich/bin/dl_poly_mpich - from package: dl_poly-mpich

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

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