openmx_mpich: command not found

Have You tried accessing the binary with the full path?

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

[root@server ~]# echo $PATH

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/openmx_mpich - from package: openmx-mpich

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