openmx_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/openmx_openmpi - from package: openmx-openmpi

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

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