esp_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/esp_openmpi - from package: openmx-openmpi

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

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